diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index 5ce9a6a9db16..92ca119895b1 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -3997,6 +3997,9 @@ gfxFontGroup* CanvasRenderingContext2D::GetCurrentFontStyle() {
     bool fontUpdated = SetFontInternal(kDefaultFontStyle, err);
     if (err.Failed() || !fontUpdated) {
       err.SuppressException();
+      // XXX Should we get a default lang from the prescontext or something?
+      nsAtom* language = nsGkAtoms::x_western;
+      bool explicitLanguage = false;
       gfxFontStyle style;
       style.size = kDefaultFontSize;
       gfxTextPerfMetrics* tp = nullptr;
@@ -4009,8 +4012,8 @@ gfxFontGroup* CanvasRenderingContext2D::GetCurrentFontStyle() {
       GetAppUnitsValues(&perDevPixel, &perCSSPixel);
       gfxFloat devToCssSize = gfxFloat(perDevPixel) / gfxFloat(perCSSPixel);
       CurrentState().fontGroup = gfxPlatform::GetPlatform()->CreateFontGroup(
-          FontFamilyList(StyleGenericFontFamily::SansSerif), &style, tp,
-          fontStats, nullptr, devToCssSize);
+          FontFamilyList(StyleGenericFontFamily::SansSerif), &style, language,
+          explicitLanguage, tp, fontStats, nullptr, devToCssSize);
       if (CurrentState().fontGroup) {
         CurrentState().font = kDefaultFontStyle;
       } else {
diff --git a/gfx/src/nsDeviceContext.cpp b/gfx/src/nsDeviceContext.cpp
index 6516af630571..daa592e1bf08 100644
--- a/gfx/src/nsDeviceContext.cpp
+++ b/gfx/src/nsDeviceContext.cpp
@@ -149,7 +149,8 @@ already_AddRefed<nsFontMetrics> nsFontCache::GetMetricsFor(
     if (fm->Font().Equals(aFont) &&
         fm->GetUserFontSet() == aParams.userFontSet &&
         fm->Language() == language &&
-        fm->Orientation() == aParams.orientation) {
+        fm->Orientation() == aParams.orientation &&
+        fm->ExplicitLanguage() == aParams.explicitLanguage) {
       if (i != n) {
         // promote it to the end of the cache
         mFontMetrics.RemoveElementAt(i);
diff --git a/gfx/src/nsFontMetrics.cpp b/gfx/src/nsFontMetrics.cpp
index 59fb7d3ce542..767b979f3a2d 100644
--- a/gfx/src/nsFontMetrics.cpp
+++ b/gfx/src/nsFontMetrics.cpp
@@ -114,12 +114,12 @@ nsFontMetrics::nsFontMetrics(const nsFont& aFont, const Params& aParams,
       mDeviceContext(aContext),
       mP2A(aContext->AppUnitsPerDevPixel()),
       mOrientation(aParams.orientation),
+      mExplicitLanguage(aParams.explicitLanguage),
       mTextRunRTL(false),
       mVertical(false),
       mTextOrientation(mozilla::StyleTextOrientation::Mixed) {
   gfxFontStyle style(aFont.style, aFont.weight, aFont.stretch,
-                     gfxFloat(aFont.size.ToAppUnits()) / mP2A, aParams.language,
-                     aParams.explicitLanguage, aFont.sizeAdjust,
+                     gfxFloat(aFont.size.ToAppUnits()) / mP2A, aFont.sizeAdjust,
                      aFont.systemFont, mDeviceContext->IsPrinterContext(),
                      aFont.synthesis & NS_FONT_SYNTHESIS_WEIGHT,
                      aFont.synthesis & NS_FONT_SYNTHESIS_STYLE,
@@ -132,8 +132,8 @@ nsFontMetrics::nsFontMetrics(const nsFont& aFont, const Params& aParams,
 
   gfxFloat devToCssSize = gfxFloat(mP2A) / gfxFloat(AppUnitsPerCSSPixel());
   mFontGroup = gfxPlatform::GetPlatform()->CreateFontGroup(
-      aFont.fontlist, &style, aParams.textPerf, aParams.fontStats,
-      aParams.userFontSet, devToCssSize);
+      aFont.fontlist, &style, mLanguage, mExplicitLanguage, aParams.textPerf,
+      aParams.fontStats, aParams.userFontSet, devToCssSize);
 }
 
 nsFontMetrics::~nsFontMetrics() {
diff --git a/gfx/src/nsFontMetrics.h b/gfx/src/nsFontMetrics.h
index 022d675865f0..b2f9554a0aef 100644
--- a/gfx/src/nsFontMetrics.h
+++ b/gfx/src/nsFontMetrics.h
@@ -235,6 +235,8 @@ class nsFontMetrics final {
     return mTextOrientation;
   }
 
+  bool ExplicitLanguage() const { return mExplicitLanguage; }
+
   gfxFontGroup* GetThebesFontGroup() const { return mFontGroup; }
   gfxUserFontSet* GetUserFontSet() const;
 
@@ -257,6 +259,11 @@ class nsFontMetrics final {
   // descent) they will return.
   FontOrientation mOrientation;
 
+  // Whether mLanguage comes from explicit markup (in which case it should be
+  // used to tailor effects like case-conversion) or is an inferred/default
+  // value.
+  bool mExplicitLanguage;
+
   // These fields may be set by clients to control the behavior of methods
   // like GetWidth and DrawString according to the writing mode, direction
   // and text-orientation desired.
diff --git a/gfx/thebes/gfxCoreTextShaper.cpp b/gfx/thebes/gfxCoreTextShaper.cpp
index ebb7498058f0..0e24337bf47e 100644
--- a/gfx/thebes/gfxCoreTextShaper.cpp
+++ b/gfx/thebes/gfxCoreTextShaper.cpp
@@ -78,7 +78,8 @@ static bool IsBuggyIndicScript(unicode::Script aScript) {
 bool gfxCoreTextShaper::ShapeText(DrawTarget* aDrawTarget,
                                   const char16_t* aText, uint32_t aOffset,
                                   uint32_t aLength, Script aScript,
-                                  bool aVertical, RoundingFlags aRounding,
+                                  nsAtom* aLanguage, bool aVertical,
+                                  RoundingFlags aRounding,
                                   gfxShapedText* aShapedText) {
   // Create a CFAttributedString with text and style info, so we can use
   // CoreText to lay it out.
diff --git a/gfx/thebes/gfxCoreTextShaper.h b/gfx/thebes/gfxCoreTextShaper.h
index c06ff73f743a..1385bd00bb12 100644
--- a/gfx/thebes/gfxCoreTextShaper.h
+++ b/gfx/thebes/gfxCoreTextShaper.h
@@ -19,7 +19,7 @@ class gfxCoreTextShaper : public gfxFontShaper {
   virtual ~gfxCoreTextShaper();
 
   bool ShapeText(DrawTarget* aDrawTarget, const char16_t* aText, uint32_t aOffset, uint32_t aLength,
-                 Script aScript, bool aVertical, RoundingFlags aRounding,
+                 Script aScript, nsAtom* aLanguage, bool aVertical, RoundingFlags aRounding,
                  gfxShapedText* aShapedText) override;
 
   // clean up static objects that may have been cached
diff --git a/gfx/thebes/gfxDWriteFontList.cpp b/gfx/thebes/gfxDWriteFontList.cpp
index 93b9beea1d25..549590a22484 100644
--- a/gfx/thebes/gfxDWriteFontList.cpp
+++ b/gfx/thebes/gfxDWriteFontList.cpp
@@ -873,7 +873,7 @@ gfxDWriteFontList::gfxDWriteFontList() : mForceGDIClassicMaxFontSize(0.0) {
 //   Arial to avoid this.
 
 FontFamily gfxDWriteFontList::GetDefaultFontForPlatform(
-    const gfxFontStyle* aStyle) {
+    const gfxFontStyle* aStyle, nsAtom* aLanguage) {
   // try Arial first
   FontFamily ff;
   ff = FindFamily("Arial"_ns);
@@ -1870,12 +1870,10 @@ void gfxDWriteFontList::GetDirectWriteSubstitutes() {
   }
 }
 
-bool gfxDWriteFontList::FindAndAddFamilies(StyleGenericFontFamily aGeneric,
-                                           const nsACString& aFamily,
-                                           nsTArray<FamilyAndGeneric>* aOutput,
-                                           FindFamiliesFlags aFlags,
-                                           gfxFontStyle* aStyle,
-                                           gfxFloat aDevToCssSize) {
+bool gfxDWriteFontList::FindAndAddFamilies(
+    StyleGenericFontFamily aGeneric, const nsACString& aFamily,
+    nsTArray<FamilyAndGeneric>* aOutput, FindFamiliesFlags aFlags,
+    gfxFontStyle* aStyle, nsAtom* aLanguage, gfxFloat aDevToCssSize) {
   nsAutoCString keyName(aFamily);
   BuildKeyNameFromFontName(keyName);
 
@@ -1896,8 +1894,8 @@ bool gfxDWriteFontList::FindAndAddFamilies(StyleGenericFontFamily aGeneric,
     return false;
   }
 
-  return gfxPlatformFontList::FindAndAddFamilies(aGeneric, keyName, aOutput,
-                                                 aFlags, aStyle, aDevToCssSize);
+  return gfxPlatformFontList::FindAndAddFamilies(
+      aGeneric, keyName, aOutput, aFlags, aStyle, aLanguage, aDevToCssSize);
 }
 
 void gfxDWriteFontList::AddSizeOfExcludingThis(MallocSizeOf aMallocSizeOf,
diff --git a/gfx/thebes/gfxDWriteFontList.h b/gfx/thebes/gfxDWriteFontList.h
index 1de880af6ae1..e6422aecddae 100644
--- a/gfx/thebes/gfxDWriteFontList.h
+++ b/gfx/thebes/gfxDWriteFontList.h
@@ -413,6 +413,7 @@ class gfxDWriteFontList final : public gfxPlatformFontList {
                           nsTArray<FamilyAndGeneric>* aOutput,
                           FindFamiliesFlags aFlags,
                           gfxFontStyle* aStyle = nullptr,
+                          nsAtom* aLanguage = nullptr,
                           gfxFloat aDevToCssSize = 1.0) override;
 
   gfxFloat GetForceGDIClassicMaxFontSize() {
@@ -425,7 +426,8 @@ class gfxDWriteFontList final : public gfxPlatformFontList {
                                       FontListSizes* aSizes) const;
 
  protected:
-  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle) override;
+  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                       nsAtom* aLanguage = nullptr) override;
 
   // attempt to use platform-specific fallback for the given character,
   // return null if no usable result found
diff --git a/gfx/thebes/gfxFT2FontList.cpp b/gfx/thebes/gfxFT2FontList.cpp
index 690e6cccdd0e..ff312d71c2dc 100644
--- a/gfx/thebes/gfxFT2FontList.cpp
+++ b/gfx/thebes/gfxFT2FontList.cpp
@@ -1737,8 +1737,8 @@ searchDone:
   return fe;
 }
 
-FontFamily gfxFT2FontList::GetDefaultFontForPlatform(
-    const gfxFontStyle* aStyle) {
+FontFamily gfxFT2FontList::GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                                     nsAtom* aLanguage) {
   FontFamily ff;
 #if defined(MOZ_WIDGET_ANDROID)
   ff = FindFamily("Roboto"_ns);
diff --git a/gfx/thebes/gfxFT2FontList.h b/gfx/thebes/gfxFT2FontList.h
index eb424c8dd551..fe87d46f9c3a 100644
--- a/gfx/thebes/gfxFT2FontList.h
+++ b/gfx/thebes/gfxFT2FontList.h
@@ -214,7 +214,8 @@ class gfxFT2FontList final : public gfxPlatformFontList {
 
   void FindFontsInDir(const nsCString& aDir, FontNameCache* aFNC);
 
-  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle) override;
+  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                       nsAtom* aLanguage = nullptr) override;
 
   nsTHashtable<nsCStringHashKey> mSkipSpaceLookupCheckFamilies;
 
diff --git a/gfx/thebes/gfxFT2Fonts.cpp b/gfx/thebes/gfxFT2Fonts.cpp
index 4cb832c1f406..b4edd2edeeaf 100644
--- a/gfx/thebes/gfxFT2Fonts.cpp
+++ b/gfx/thebes/gfxFT2Fonts.cpp
@@ -42,10 +42,11 @@ using namespace mozilla::gfx;
 
 bool gfxFT2Font::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                            uint32_t aOffset, uint32_t aLength, Script aScript,
-                           bool aVertical, RoundingFlags aRounding,
+                           nsAtom* aLanguage, bool aVertical,
+                           RoundingFlags aRounding,
                            gfxShapedText* aShapedText) {
   if (!gfxFont::ShapeText(aDrawTarget, aText, aOffset, aLength, aScript,
-                          aVertical, aRounding, aShapedText)) {
+                          aLanguage, aVertical, aRounding, aShapedText)) {
     // harfbuzz must have failed(?!), just render raw glyphs
     AddRange(aText, aOffset, aLength, aShapedText);
     PostShapingFixup(aDrawTarget, aText, aOffset, aLength, aVertical,
diff --git a/gfx/thebes/gfxFT2Fonts.h b/gfx/thebes/gfxFT2Fonts.h
index 031864a1b94b..65699b27b75a 100644
--- a/gfx/thebes/gfxFT2Fonts.h
+++ b/gfx/thebes/gfxFT2Fonts.h
@@ -63,7 +63,7 @@ class gfxFT2Font : public gfxFT2FontBase {
 
   bool ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                  uint32_t aOffset, uint32_t aLength, Script aScript,
-                 bool aVertical, RoundingFlags aRounding,
+                 nsAtom* aLanguage, bool aVertical, RoundingFlags aRounding,
                  gfxShapedText* aShapedText) override;
 
   void FillGlyphDataForChar(FT_Face face, uint32_t ch, CachedGlyphData* gd);
diff --git a/gfx/thebes/gfxFcPlatformFontList.cpp b/gfx/thebes/gfxFcPlatformFontList.cpp
index f4fff2339212..3d9fa8b062f9 100644
--- a/gfx/thebes/gfxFcPlatformFontList.cpp
+++ b/gfx/thebes/gfxFcPlatformFontList.cpp
@@ -1856,11 +1856,11 @@ void gfxFcPlatformFontList::GetFontList(nsAtom* aLangGroup,
 }
 
 FontFamily gfxFcPlatformFontList::GetDefaultFontForPlatform(
-    const gfxFontStyle* aStyle) {
+    const gfxFontStyle* aStyle, nsAtom* aLanguage) {
   // Get the default font by using a fake name to retrieve the first
   // scalable font that fontconfig suggests for the given language.
-  PrefFontList* prefFonts =
-      FindGenericFamilies("-moz-default"_ns, aStyle->language);
+  PrefFontList* prefFonts = FindGenericFamilies(
+      "-moz-default"_ns, aLanguage ? aLanguage : nsGkAtoms::x_western);
   NS_ASSERTION(prefFonts, "null list of generic fonts");
   if (prefFonts && !prefFonts->IsEmpty()) {
     return (*prefFonts)[0];
@@ -1906,10 +1906,9 @@ gfxFontEntry* gfxFcPlatformFontList::MakePlatformFont(
 bool gfxFcPlatformFontList::FindAndAddFamilies(
     StyleGenericFontFamily aGeneric, const nsACString& aFamily,
     nsTArray<FamilyAndGeneric>* aOutput, FindFamiliesFlags aFlags,
-    gfxFontStyle* aStyle, gfxFloat aDevToCssSize) {
+    gfxFontStyle* aStyle, nsAtom* aLanguage, gfxFloat aDevToCssSize) {
   nsAutoCString familyName(aFamily);
   ToLowerCase(familyName);
-  nsAtom* language = (aStyle ? aStyle->language.get() : nullptr);
 
   if (!(aFlags & FindFamiliesFlags::eQuotedFamilyName)) {
     // deprecated generic names are explicitly converted to standard generics
@@ -1926,7 +1925,7 @@ bool gfxFcPlatformFontList::FindAndAddFamilies(
     // fontconfig generics? use fontconfig to determine the family for lang
     if (isDeprecatedGeneric ||
         mozilla::FontFamilyName::Convert(familyName).IsGeneric()) {
-      PrefFontList* prefFonts = FindGenericFamilies(familyName, language);
+      PrefFontList* prefFonts = FindGenericFamilies(familyName, aLanguage);
       if (prefFonts && !prefFonts->IsEmpty()) {
         aOutput->AppendElements(*prefFonts);
         return true;
@@ -1986,7 +1985,7 @@ bool gfxFcPlatformFontList::FindAndAddFamilies(
     }
     gfxPlatformFontList::FindAndAddFamilies(
         aGeneric, nsDependentCString(ToCharPtr(substName)), &cachedFamilies,
-        aFlags);
+        aFlags, aStyle, aLanguage);
   }
 
   // Cache the resulting list, so we don't have to do this again.
diff --git a/gfx/thebes/gfxFcPlatformFontList.h b/gfx/thebes/gfxFcPlatformFontList.h
index cf13b3d9b847..e5803e0b3441 100644
--- a/gfx/thebes/gfxFcPlatformFontList.h
+++ b/gfx/thebes/gfxFcPlatformFontList.h
@@ -266,6 +266,7 @@ class gfxFcPlatformFontList final : public gfxPlatformFontList {
                           nsTArray<FamilyAndGeneric>* aOutput,
                           FindFamiliesFlags aFlags,
                           gfxFontStyle* aStyle = nullptr,
+                          nsAtom* aLanguage = nullptr,
                           gfxFloat aDevToCssSize = 1.0) override;
 
   bool GetStandardFamilyName(const nsCString& aFontName,
@@ -320,7 +321,8 @@ class gfxFcPlatformFontList final : public gfxPlatformFontList {
 
   static void CheckFontUpdates(nsITimer* aTimer, void* aThis);
 
-  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle) override;
+  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                       nsAtom* aLanguage = nullptr) override;
 
   enum class DistroID : int8_t {
     Unknown = 0,
diff --git a/gfx/thebes/gfxFont.cpp b/gfx/thebes/gfxFont.cpp
index 0eac5a0f0f69..d169297e3cec 100644
--- a/gfx/thebes/gfxFont.cpp
+++ b/gfx/thebes/gfxFont.cpp
@@ -2732,9 +2732,9 @@ static char16_t IsBoundarySpace(char16_t aChar, char16_t aNextChar) {
 template <typename T>
 gfxShapedWord* gfxFont::GetShapedWord(
     DrawTarget* aDrawTarget, const T* aText, uint32_t aLength, uint32_t aHash,
-    Script aRunScript, bool aVertical, int32_t aAppUnitsPerDevUnit,
-    gfx::ShapedTextFlags aFlags, RoundingFlags aRounding,
-    gfxTextPerfMetrics* aTextPerf GFX_MAYBE_UNUSED) {
+    Script aRunScript, nsAtom* aLanguage, bool aVertical,
+    int32_t aAppUnitsPerDevUnit, gfx::ShapedTextFlags aFlags,
+    RoundingFlags aRounding, gfxTextPerfMetrics* aTextPerf GFX_MAYBE_UNUSED) {
   // if the cache is getting too big, flush it and start over
   uint32_t wordCacheMaxEntries =
       gfxPlatform::GetPlatform()->WordCacheMaxEntries();
@@ -2744,8 +2744,8 @@ gfxShapedWord* gfxFont::GetShapedWord(
   }
 
   // if there's a cached entry for this word, just return it
-  CacheHashKey key(aText, aLength, aHash, aRunScript, aAppUnitsPerDevUnit,
-                   aFlags, aRounding);
+  CacheHashKey key(aText, aLength, aHash, aRunScript, aLanguage,
+                   aAppUnitsPerDevUnit, aFlags, aRounding);
 
   CacheHashEntry* entry = mWordCache->PutEntry(key, fallible);
   if (!entry) {
@@ -2770,8 +2770,8 @@ gfxShapedWord* gfxFont::GetShapedWord(
   }
 #endif
 
-  sw = gfxShapedWord::Create(aText, aLength, aRunScript, aAppUnitsPerDevUnit,
-                             aFlags, aRounding);
+  sw = gfxShapedWord::Create(aText, aLength, aRunScript, aLanguage,
+                             aAppUnitsPerDevUnit, aFlags, aRounding);
   entry->mShapedWord.reset(sw);
   if (!sw) {
     NS_WARNING("failed to create gfxShapedWord - expect missing text");
@@ -2779,7 +2779,7 @@ gfxShapedWord* gfxFont::GetShapedWord(
   }
 
   DebugOnly<bool> ok = ShapeText(aDrawTarget, aText, 0, aLength, aRunScript,
-                                 aVertical, aRounding, sw);
+                                 aLanguage, aVertical, aRounding, sw);
 
   NS_WARNING_ASSERTION(ok, "failed to shape word - expect garbled text");
 
@@ -2788,7 +2788,7 @@ gfxShapedWord* gfxFont::GetShapedWord(
 
 template gfxShapedWord* gfxFont::GetShapedWord(
     DrawTarget* aDrawTarget, const uint8_t* aText, uint32_t aLength,
-    uint32_t aHash, Script aRunScript, bool aVertical,
+    uint32_t aHash, Script aRunScript, nsAtom* aLanguage, bool aVertical,
     int32_t aAppUnitsPerDevUnit, gfx::ShapedTextFlags aFlags,
     RoundingFlags aRounding, gfxTextPerfMetrics* aTextPerf);
 
@@ -2800,7 +2800,8 @@ bool gfxFont::CacheHashEntry::KeyEquals(const KeyTypePointer aKey) const {
   if (sw->GetLength() != aKey->mLength || sw->GetFlags() != aKey->mFlags ||
       sw->GetRounding() != aKey->mRounding ||
       sw->GetAppUnitsPerDevUnit() != aKey->mAppUnitsPerDevUnit ||
-      sw->GetScript() != aKey->mScript) {
+      sw->GetScript() != aKey->mScript ||
+      sw->GetLanguage() != aKey->mLanguage) {
     return false;
   }
   if (sw->TextIs8Bit()) {
@@ -2830,8 +2831,8 @@ bool gfxFont::CacheHashEntry::KeyEquals(const KeyTypePointer aKey) const {
 
 bool gfxFont::ShapeText(DrawTarget* aDrawTarget, const uint8_t* aText,
                         uint32_t aOffset, uint32_t aLength, Script aScript,
-                        bool aVertical, RoundingFlags aRounding,
-                        gfxShapedText* aShapedText) {
+                        nsAtom* aLanguage, bool aVertical,
+                        RoundingFlags aRounding, gfxShapedText* aShapedText) {
   nsDependentCSubstring ascii((const char*)aText, aLength);
   nsAutoString utf16;
   AppendASCIItoUTF16(ascii, utf16);
@@ -2839,13 +2840,13 @@ bool gfxFont::ShapeText(DrawTarget* aDrawTarget, const uint8_t* aText,
     return false;
   }
   return ShapeText(aDrawTarget, utf16.BeginReading(), aOffset, aLength, aScript,
-                   aVertical, aRounding, aShapedText);
+                   aLanguage, aVertical, aRounding, aShapedText);
 }
 
 bool gfxFont::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                         uint32_t aOffset, uint32_t aLength, Script aScript,
-                        bool aVertical, RoundingFlags aRounding,
-                        gfxShapedText* aShapedText) {
+                        nsAtom* aLanguage, bool aVertical,
+                        RoundingFlags aRounding, gfxShapedText* aShapedText) {
   // XXX Currently, we do all vertical shaping through harfbuzz.
   // Vertical graphite support may be wanted as a future enhancement.
   if (FontCanSupportGraphite() && !aVertical) {
@@ -2855,7 +2856,7 @@ bool gfxFont::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
         Telemetry::ScalarAdd(Telemetry::ScalarID::BROWSER_USAGE_GRAPHITE, 1);
       }
       if (mGraphiteShaper->ShapeText(aDrawTarget, aText, aOffset, aLength,
-                                     aScript, aVertical, aRounding,
+                                     aScript, aLanguage, aVertical, aRounding,
                                      aShapedText)) {
         PostShapingFixup(aDrawTarget, aText, aOffset, aLength, aVertical,
                          aShapedText);
@@ -2868,7 +2869,8 @@ bool gfxFont::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
     mHarfBuzzShaper = MakeUnique<gfxHarfBuzzShaper>(this);
   }
   if (mHarfBuzzShaper->ShapeText(aDrawTarget, aText, aOffset, aLength, aScript,
-                                 aVertical, aRounding, aShapedText)) {
+                                 aLanguage, aVertical, aRounding,
+                                 aShapedText)) {
     PostShapingFixup(aDrawTarget, aText, aOffset, aLength, aVertical,
                      aShapedText);
     if (GetFontEntry()->HasTrackingTable()) {
@@ -2917,7 +2919,7 @@ template <typename T>
 bool gfxFont::ShapeFragmentWithoutWordCache(DrawTarget* aDrawTarget,
                                             const T* aText, uint32_t aOffset,
                                             uint32_t aLength, Script aScript,
-                                            bool aVertical,
+                                            nsAtom* aLanguage, bool aVertical,
                                             RoundingFlags aRounding,
                                             gfxTextRun* aTextRun) {
   aTextRun->SetupClusterBoundaries(aOffset, aText, aLength);
@@ -2952,8 +2954,8 @@ bool gfxFont::ShapeFragmentWithoutWordCache(DrawTarget* aDrawTarget,
       }
     }
 
-    ok = ShapeText(aDrawTarget, aText, aOffset, fragLen, aScript, aVertical,
-                   aRounding, aTextRun);
+    ok = ShapeText(aDrawTarget, aText, aOffset, fragLen, aScript, aLanguage,
+                   aVertical, aRounding, aTextRun);
 
     aText += fragLen;
     aOffset += fragLen;
@@ -2975,8 +2977,8 @@ static bool IsInvalidControlChar(uint32_t aCh) {
 template <typename T>
 bool gfxFont::ShapeTextWithoutWordCache(DrawTarget* aDrawTarget, const T* aText,
                                         uint32_t aOffset, uint32_t aLength,
-                                        Script aScript, bool aVertical,
-                                        RoundingFlags aRounding,
+                                        Script aScript, nsAtom* aLanguage,
+                                        bool aVertical, RoundingFlags aRounding,
                                         gfxTextRun* aTextRun) {
   uint32_t fragStart = 0;
   bool ok = true;
@@ -2992,9 +2994,9 @@ bool gfxFont::ShapeTextWithoutWordCache(DrawTarget* aDrawTarget, const T* aText,
     }
 
     if (length > 0) {
-      ok = ShapeFragmentWithoutWordCache(aDrawTarget, aText + fragStart,
-                                         aOffset + fragStart, length, aScript,
-                                         aVertical, aRounding, aTextRun);
+      ok = ShapeFragmentWithoutWordCache(
+          aDrawTarget, aText + fragStart, aOffset + fragStart, length, aScript,
+          aLanguage, aVertical, aRounding, aTextRun);
     }
 
     if (i == aLength) {
@@ -3015,7 +3017,8 @@ bool gfxFont::ShapeTextWithoutWordCache(DrawTarget* aDrawTarget, const T* aText,
                  gfx::ShapedTextFlags::TEXT_HIDE_CONTROL_CHARACTERS)) {
       if (GetFontEntry()->IsUserFont() && HasCharacter(ch)) {
         ShapeFragmentWithoutWordCache(aDrawTarget, aText + i, aOffset + i, 1,
-                                      aScript, aVertical, aRounding, aTextRun);
+                                      aScript, aLanguage, aVertical, aRounding,
+                                      aTextRun);
       } else {
         aTextRun->SetMissingGlyph(aOffset + i, ch, this);
       }
@@ -3054,7 +3057,8 @@ bool gfxFont::SplitAndInitTextRun(
     DrawTarget* aDrawTarget, gfxTextRun* aTextRun,
     const T* aString,    // text for this font run
     uint32_t aRunStart,  // position in the textrun
-    uint32_t aRunLength, Script aRunScript, ShapedTextFlags aOrientation) {
+    uint32_t aRunLength, Script aRunScript, nsAtom* aLanguage,
+    ShapedTextFlags aOrientation) {
   if (aRunLength == 0) {
     return true;
   }
@@ -3099,8 +3103,8 @@ bool gfxFont::SplitAndInitTextRun(
     if (aRunLength > wordCacheCharLimit || HasSpaces(aString, aRunLength)) {
       TEXT_PERF_INCR(tp, wordCacheSpaceRules);
       return ShapeTextWithoutWordCache(aDrawTarget, aString, aRunStart,
-                                       aRunLength, aRunScript, vertical,
-                                       rounding, aTextRun);
+                                       aRunLength, aRunScript, aLanguage,
+                                       vertical, rounding, aTextRun);
     }
   }
 
@@ -3149,7 +3153,7 @@ bool gfxFont::SplitAndInitTextRun(
       TEXT_PERF_INCR(tp, wordCacheLong);
       bool ok = ShapeFragmentWithoutWordCache(
           aDrawTarget, aString + wordStart, aRunStart + wordStart, length,
-          aRunScript, vertical, rounding, aTextRun);
+          aRunScript, aLanguage, vertical, rounding, aTextRun);
       if (!ok) {
         return false;
       }
@@ -3164,8 +3168,8 @@ bool gfxFont::SplitAndInitTextRun(
         }
       }
       gfxShapedWord* sw = GetShapedWord(
-          aDrawTarget, aString + wordStart, length, hash, aRunScript, vertical,
-          appUnitsPerDevUnit, wordFlags, rounding, tp);
+          aDrawTarget, aString + wordStart, length, hash, aRunScript, aLanguage,
+          vertical, appUnitsPerDevUnit, wordFlags, rounding, tp);
       if (sw) {
         aTextRun->CopyGlyphDataFrom(sw, aRunStart + wordStart);
       } else {
@@ -3188,7 +3192,7 @@ bool gfxFont::SplitAndInitTextRun(
         NS_ASSERTION(boundary16 < 256, "unexpected boundary!");
         gfxShapedWord* sw = GetShapedWord(
             aDrawTarget, &boundary, 1, gfxShapedWord::HashMix(0, boundary),
-            aRunScript, vertical, appUnitsPerDevUnit,
+            aRunScript, aLanguage, vertical, appUnitsPerDevUnit,
             flags | gfx::ShapedTextFlags::TEXT_IS_8BIT, rounding, tp);
         if (sw) {
           aTextRun->CopyGlyphDataFrom(sw, aRunStart + i);
@@ -3225,8 +3229,8 @@ bool gfxFont::SplitAndInitTextRun(
                  gfx::ShapedTextFlags::TEXT_HIDE_CONTROL_CHARACTERS)) {
       if (GetFontEntry()->IsUserFont() && HasCharacter(ch)) {
         ShapeFragmentWithoutWordCache(aDrawTarget, aString + i, aRunStart + i,
-                                      1, aRunScript, vertical, rounding,
-                                      aTextRun);
+                                      1, aRunScript, aLanguage, vertical,
+                                      rounding, aTextRun);
       } else {
         aTextRun->SetMissingGlyph(aRunStart + i, ch, this);
       }
@@ -3244,11 +3248,11 @@ bool gfxFont::SplitAndInitTextRun(
 template bool gfxFont::SplitAndInitTextRun(
     DrawTarget* aDrawTarget, gfxTextRun* aTextRun, const uint8_t* aString,
     uint32_t aRunStart, uint32_t aRunLength, Script aRunScript,
-    ShapedTextFlags aOrientation);
+    nsAtom* aLanguage, ShapedTextFlags aOrientation);
 template bool gfxFont::SplitAndInitTextRun(
     DrawTarget* aDrawTarget, gfxTextRun* aTextRun, const char16_t* aString,
     uint32_t aRunStart, uint32_t aRunLength, Script aRunScript,
-    ShapedTextFlags aOrientation);
+    nsAtom* aLanguage, ShapedTextFlags aOrientation);
 
 template <>
 bool gfxFont::InitFakeSmallCapsRun(DrawTarget* aDrawTarget,
@@ -3256,8 +3260,8 @@ bool gfxFont::InitFakeSmallCapsRun(DrawTarget* aDrawTarget,
                                    uint32_t aOffset, uint32_t aLength,
                                    FontMatchType aMatchType,
                                    gfx::ShapedTextFlags aOrientation,
-                                   Script aScript, bool aSyntheticLower,
-                                   bool aSyntheticUpper) {
+                                   Script aScript, nsAtom* aLanguage,
+                                   bool aSyntheticLower, bool aSyntheticUpper) {
   bool ok = true;
 
   RefPtr<gfxFont> smallCapsFont = GetSmallCapsFont();
@@ -3297,7 +3301,7 @@ bool gfxFont::InitFakeSmallCapsRun(DrawTarget* aDrawTarget,
         } else if (ch != ToLowerCase(ch)) {
           // ch is upper case
           chAction = (aSyntheticUpper ? kUppercaseReduce : kNoChange);
-          if (mStyle.explicitLanguage && mStyle.language == nsGkAtoms::el) {
+          if (aLanguage == nsGkAtoms::el) {
             // In Greek, check for characters that will be modified by
             // the GreekUpperCase mapping - this catches accented
             // capitals where the accent is to be removed (bug 307039).
@@ -3330,7 +3334,7 @@ bool gfxFont::InitFakeSmallCapsRun(DrawTarget* aDrawTarget,
                                 aOrientation, isCJK);
           if (!f->SplitAndInitTextRun(aDrawTarget, aTextRun, aText + runStart,
                                       aOffset + runStart, runLength, aScript,
-                                      aOrientation)) {
+                                      aLanguage, aOrientation)) {
             ok = false;
           }
           break;
@@ -3349,9 +3353,8 @@ bool gfxFont::InitFakeSmallCapsRun(DrawTarget* aDrawTarget,
 
           bool mergeNeeded = nsCaseTransformTextRunFactory::TransformString(
               origString, convertedString, /* aAllUppercase = */ true,
-              /* aCaseTransformsOnly = */ false,
-              mStyle.explicitLanguage ? mStyle.language.get() : nullptr,
-              charsToMergeArray, deletedCharsArray);
+              /* aCaseTransformsOnly = */ false, aLanguage, charsToMergeArray,
+              deletedCharsArray);
 
           if (mergeNeeded) {
             // This is the hard case: the transformation caused chars
@@ -3365,9 +3368,10 @@ bool gfxFont::InitFakeSmallCapsRun(DrawTarget* aDrawTarget,
                 &params, convertedString.Length(), aTextRun->GetFontGroup(),
                 gfx::ShapedTextFlags(), nsTextFrameUtils::Flags()));
             tempRun->AddGlyphRun(f, aMatchType, 0, true, aOrientation, isCJK);
-            if (!f->SplitAndInitTextRun(
-                    aDrawTarget, tempRun.get(), convertedString.BeginReading(),
-                    0, convertedString.Length(), aScript, aOrientation)) {
+            if (!f->SplitAndInitTextRun(aDrawTarget, tempRun.get(),
+                                        convertedString.BeginReading(), 0,
+                                        convertedString.Length(), aScript,
+                                        aLanguage, aOrientation)) {
               ok = false;
             } else {
               RefPtr<gfxTextRun> mergedRun(gfxTextRun::Create(
@@ -3383,9 +3387,10 @@ bool gfxFont::InitFakeSmallCapsRun(DrawTarget* aDrawTarget,
           } else {
             aTextRun->AddGlyphRun(f, aMatchType, aOffset + runStart, true,
                                   aOrientation, isCJK);
-            if (!f->SplitAndInitTextRun(
-                    aDrawTarget, aTextRun, convertedString.BeginReading(),
-                    aOffset + runStart, runLength, aScript, aOrientation)) {
+            if (!f->SplitAndInitTextRun(aDrawTarget, aTextRun,
+                                        convertedString.BeginReading(),
+                                        aOffset + runStart, runLength, aScript,
+                                        aLanguage, aOrientation)) {
               ok = false;
             }
           }
@@ -3410,14 +3415,14 @@ bool gfxFont::InitFakeSmallCapsRun(DrawTarget* aDrawTarget,
                                    uint32_t aOffset, uint32_t aLength,
                                    FontMatchType aMatchType,
                                    gfx::ShapedTextFlags aOrientation,
-                                   Script aScript, bool aSyntheticLower,
-                                   bool aSyntheticUpper) {
+                                   Script aScript, nsAtom* aLanguage,
+                                   bool aSyntheticLower, bool aSyntheticUpper) {
   NS_ConvertASCIItoUTF16 unicodeString(reinterpret_cast<const char*>(aText),
                                        aLength);
-  return InitFakeSmallCapsRun(aDrawTarget, aTextRun,
-                              static_cast<const char16_t*>(unicodeString.get()),
-                              aOffset, aLength, aMatchType, aOrientation,
-                              aScript, aSyntheticLower, aSyntheticUpper);
+  return InitFakeSmallCapsRun(
+      aDrawTarget, aTextRun, static_cast<const char16_t*>(unicodeString.get()),
+      aOffset, aLength, aMatchType, aOrientation, aScript, aLanguage,
+      aSyntheticLower, aSyntheticUpper);
 }
 
 gfxFont* gfxFont::GetSmallCapsFont() {
@@ -3968,8 +3973,7 @@ void gfxFont::RemoveGlyphChangeObserver(GlyphChangeObserver* aObserver) {
 #define DEFAULT_PIXEL_FONT_SIZE 16.0f
 
 gfxFontStyle::gfxFontStyle()
-    : language(nsGkAtoms::x_western),
-      size(DEFAULT_PIXEL_FONT_SIZE),
+    : size(DEFAULT_PIXEL_FONT_SIZE),
       sizeAdjust(-1.0f),
       baselineOffset(0.0f),
       languageOverride(NO_FONT_LANGUAGE_OVERRIDE),
@@ -3984,18 +3988,15 @@ gfxFontStyle::gfxFontStyle()
       useGrayscaleAntialiasing(false),
       allowSyntheticWeight(true),
       allowSyntheticStyle(true),
-      noFallbackVariantFeatures(true),
-      explicitLanguage(false) {}
+      noFallbackVariantFeatures(true) {}
 
 gfxFontStyle::gfxFontStyle(FontSlantStyle aStyle, FontWeight aWeight,
                            FontStretch aStretch, gfxFloat aSize,
-                           nsAtom* aLanguage, bool aExplicitLanguage,
                            float aSizeAdjust, bool aSystemFont,
                            bool aPrinterFont, bool aAllowWeightSynthesis,
                            bool aAllowStyleSynthesis,
                            uint32_t aLanguageOverride)
-    : language(aLanguage),
-      size(aSize),
+    : size(aSize),
       sizeAdjust(aSizeAdjust),
       baselineOffset(0.0f),
       languageOverride(aLanguageOverride),
@@ -4010,8 +4011,7 @@ gfxFontStyle::gfxFontStyle(FontSlantStyle aStyle, FontWeight aWeight,
       useGrayscaleAntialiasing(false),
       allowSyntheticWeight(aAllowWeightSynthesis),
       allowSyntheticStyle(aAllowStyleSynthesis),
-      noFallbackVariantFeatures(true),
-      explicitLanguage(aExplicitLanguage) {
+      noFallbackVariantFeatures(true) {
   MOZ_ASSERT(!mozilla::IsNaN(size));
   MOZ_ASSERT(!mozilla::IsNaN(sizeAdjust));
 
@@ -4029,11 +4029,6 @@ gfxFontStyle::gfxFontStyle(FontSlantStyle aStyle, FontWeight aWeight,
     NS_WARNING("negative font size");
     size = 0.0;
   }
-
-  if (!language) {
-    NS_WARNING("null language");
-    language = nsGkAtoms::x_western;
-  }
 }
 
 PLDHashNumber gfxFontStyle::Hash() const {
@@ -4044,8 +4039,7 @@ PLDHashNumber gfxFontStyle::Hash() const {
                                                sizeof(gfxFontVariation));
   return mozilla::AddToHash(hash, systemFont, style.ForHash(),
                             stretch.ForHash(), weight.ForHash(), size,
-                            int32_t(sizeAdjust * 1000.0f),
-                            nsRefPtrHashKey<nsAtom>::HashKey(language));
+                            int32_t(sizeAdjust * 1000.0f));
 }
 
 void gfxFontStyle::AdjustForSubSuperscript(int32_t aAppUnitsPerDevPixel) {
diff --git a/gfx/thebes/gfxFont.h b/gfx/thebes/gfxFont.h
index 526bd7e700f4..636883e8a4ee 100644
--- a/gfx/thebes/gfxFont.h
+++ b/gfx/thebes/gfxFont.h
@@ -79,16 +79,9 @@ struct gfxFontStyle {
 
   gfxFontStyle();
   gfxFontStyle(FontSlantStyle aStyle, FontWeight aWeight, FontStretch aStretch,
-               gfxFloat aSize, nsAtom* aLanguage, bool aExplicitLanguage,
-               float aSizeAdjust, bool aSystemFont, bool aPrinterFont,
-               bool aWeightSynthesis, bool aStyleSynthesis,
+               gfxFloat aSize, float aSizeAdjust, bool aSystemFont,
+               bool aPrinterFont, bool aWeightSynthesis, bool aStyleSynthesis,
                uint32_t aLanguageOverride);
-
-  // the language (may be an internal langGroup code rather than an actual
-  // language code) specified in the document or element's lang property,
-  // or inferred from the charset
-  RefPtr<nsAtom> language;
-
   // Features are composed of (1) features from style rules (2) features
   // from feature settings rules and (3) family-specific features.  (1) and
   // (3) are guaranteed to be mutually exclusive
@@ -182,10 +175,6 @@ struct gfxFontStyle {
   // code, so set up a bool to indicate when shaping with fallback is needed
   bool noFallbackVariantFeatures : 1;
 
-  // whether the |language| field comes from explicit lang tagging in the
-  // document, or was inferred from charset/system locale
-  bool explicitLanguage : 1;
-
   // Return the final adjusted font size for the given aspect ratio.
   // Not meant to be called when sizeAdjust = -1.0.
   gfxFloat GetAdjustedSize(gfxFloat aspect) const {
@@ -219,8 +208,6 @@ struct gfxFontStyle {
            (systemFont == other.systemFont) &&
            (printerFont == other.printerFont) &&
            (useGrayscaleAntialiasing == other.useGrayscaleAntialiasing) &&
-           (explicitLanguage == other.explicitLanguage) &&
-           (language == other.language) &&
            (baselineOffset == other.baselineOffset) &&
            (*reinterpret_cast<const uint32_t*>(&sizeAdjust) ==
             *reinterpret_cast<const uint32_t*>(&other.sizeAdjust)) &&
@@ -641,6 +628,9 @@ class gfxFontShaper {
   // aShapedText to be updated; aLength is also the length of aText.
   virtual bool ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                          uint32_t aOffset, uint32_t aLength, Script aScript,
+                         nsAtom* aLanguage,  // may be null, indicating no
+                                             // lang-specific shaping to be
+                                             // applied
                          bool aVertical, RoundingFlags aRounding,
                          gfxShapedText* aShapedText) = 0;
 
@@ -1224,7 +1214,8 @@ class gfxShapedWord final : public gfxShapedText {
   // glyph data; the caller must call gfxFont::ShapeText() with appropriate
   // parameters to set up the glyphs.
   static gfxShapedWord* Create(const uint8_t* aText, uint32_t aLength,
-                               Script aRunScript, uint16_t aAppUnitsPerDevUnit,
+                               Script aRunScript, nsAtom* aLanguage,
+                               uint16_t aAppUnitsPerDevUnit,
                                mozilla::gfx::ShapedTextFlags aFlags,
                                gfxFontShaper::RoundingFlags aRounding) {
     NS_ASSERTION(aLength <= gfxPlatform::GetPlatform()->WordCacheCharLimit(),
@@ -1240,12 +1231,13 @@ class gfxShapedWord final : public gfxShapedText {
     }
 
     // Construct in the pre-allocated storage, using placement new
-    return new (storage) gfxShapedWord(aText, aLength, aRunScript,
+    return new (storage) gfxShapedWord(aText, aLength, aRunScript, aLanguage,
                                        aAppUnitsPerDevUnit, aFlags, aRounding);
   }
 
   static gfxShapedWord* Create(const char16_t* aText, uint32_t aLength,
-                               Script aRunScript, uint16_t aAppUnitsPerDevUnit,
+                               Script aRunScript, nsAtom* aLanguage,
+                               uint16_t aAppUnitsPerDevUnit,
                                mozilla::gfx::ShapedTextFlags aFlags,
                                gfxFontShaper::RoundingFlags aRounding) {
     NS_ASSERTION(aLength <= gfxPlatform::GetPlatform()->WordCacheCharLimit(),
@@ -1258,7 +1250,8 @@ class gfxShapedWord final : public gfxShapedText {
       nsAutoCString narrowText;
       LossyAppendUTF16toASCII(nsDependentSubstring(aText, aLength), narrowText);
       return Create((const uint8_t*)(narrowText.BeginReading()), aLength,
-                    aRunScript, aAppUnitsPerDevUnit, aFlags, aRounding);
+                    aRunScript, aLanguage, aAppUnitsPerDevUnit, aFlags,
+                    aRounding);
     }
 
     uint32_t size = offsetof(gfxShapedWord, mCharGlyphsStorage) +
@@ -1268,7 +1261,7 @@ class gfxShapedWord final : public gfxShapedText {
       return nullptr;
     }
 
-    return new (storage) gfxShapedWord(aText, aLength, aRunScript,
+    return new (storage) gfxShapedWord(aText, aLength, aRunScript, aLanguage,
                                        aAppUnitsPerDevUnit, aFlags, aRounding);
   }
 
@@ -1300,6 +1293,7 @@ class gfxShapedWord final : public gfxShapedText {
   }
 
   Script GetScript() const { return mScript; }
+  nsAtom* GetLanguage() const { return mLanguage.get(); }
 
   gfxFontShaper::RoundingFlags GetRounding() const { return mRounding; }
 
@@ -1317,12 +1311,13 @@ class gfxShapedWord final : public gfxShapedText {
 
   // Construct storage for a ShapedWord, ready to receive glyph data
   gfxShapedWord(const uint8_t* aText, uint32_t aLength, Script aRunScript,
-                uint16_t aAppUnitsPerDevUnit,
+                nsAtom* aLanguage, uint16_t aAppUnitsPerDevUnit,
                 mozilla::gfx::ShapedTextFlags aFlags,
                 gfxFontShaper::RoundingFlags aRounding)
       : gfxShapedText(aLength,
                       aFlags | mozilla::gfx::ShapedTextFlags::TEXT_IS_8BIT,
                       aAppUnitsPerDevUnit),
+        mLanguage(aLanguage),
         mScript(aRunScript),
         mRounding(aRounding),
         mAgeCounter(0) {
@@ -1332,10 +1327,11 @@ class gfxShapedWord final : public gfxShapedText {
   }
 
   gfxShapedWord(const char16_t* aText, uint32_t aLength, Script aRunScript,
-                uint16_t aAppUnitsPerDevUnit,
+                nsAtom* aLanguage, uint16_t aAppUnitsPerDevUnit,
                 mozilla::gfx::ShapedTextFlags aFlags,
                 gfxFontShaper::RoundingFlags aRounding)
       : gfxShapedText(aLength, aFlags, aAppUnitsPerDevUnit),
+        mLanguage(aLanguage),
         mScript(aRunScript),
         mRounding(aRounding),
         mAgeCounter(0) {
@@ -1345,6 +1341,7 @@ class gfxShapedWord final : public gfxShapedText {
     SetupClusterBoundaries(0, aText, aLength);
   }
 
+  RefPtr<nsAtom> mLanguage;
   Script mScript;
 
   gfxFontShaper::RoundingFlags mRounding;
@@ -1755,8 +1752,8 @@ class gfxFont {
                             const T* aText, uint32_t aOffset, uint32_t aLength,
                             FontMatchType aMatchType,
                             mozilla::gfx::ShapedTextFlags aOrientation,
-                            Script aScript, bool aSyntheticLower,
-                            bool aSyntheticUpper);
+                            Script aScript, nsAtom* aLanguage,
+                            bool aSyntheticLower, bool aSyntheticUpper);
 
   // call the (virtual) InitTextRun method to do glyph generation/shaping,
   // limiting the length of text passed by processing the run in multiple
@@ -1765,6 +1762,7 @@ class gfxFont {
   bool SplitAndInitTextRun(DrawTarget* aDrawTarget, gfxTextRun* aTextRun,
                            const T* aString, uint32_t aRunStart,
                            uint32_t aRunLength, Script aRunScript,
+                           nsAtom* aLanguage,
                            mozilla::gfx::ShapedTextFlags aOrientation);
 
   // Get a ShapedWord representing the given text (either 8- or 16-bit)
@@ -1772,8 +1770,8 @@ class gfxFont {
   template <typename T>
   gfxShapedWord* GetShapedWord(DrawTarget* aDrawTarget, const T* aText,
                                uint32_t aLength, uint32_t aHash,
-                               Script aRunScript, bool aVertical,
-                               int32_t aAppUnitsPerDevUnit,
+                               Script aRunScript, nsAtom* aLanguage,
+                               bool aVertical, int32_t aAppUnitsPerDevUnit,
                                mozilla::gfx::ShapedTextFlags aFlags,
                                RoundingFlags aRounding,
                                gfxTextPerfMetrics* aTextPerf);
@@ -1961,16 +1959,16 @@ class gfxFont {
   // For 8-bit text, expand to 16-bit and then call the following method.
   bool ShapeText(DrawTarget* aContext, const uint8_t* aText,
                  uint32_t aOffset,  // dest offset in gfxShapedText
-                 uint32_t aLength, Script aScript, bool aVertical,
-                 RoundingFlags aRounding,
+                 uint32_t aLength, Script aScript, nsAtom* aLanguage,
+                 bool aVertical, RoundingFlags aRounding,
                  gfxShapedText* aShapedText);  // where to store the result
 
   // Call the appropriate shaper to generate glyphs for aText and store
   // them into aShapedText.
   virtual bool ShapeText(DrawTarget* aContext, const char16_t* aText,
                          uint32_t aOffset, uint32_t aLength, Script aScript,
-                         bool aVertical, RoundingFlags aRounding,
-                         gfxShapedText* aShapedText);
+                         nsAtom* aLanguage, bool aVertical,
+                         RoundingFlags aRounding, gfxShapedText* aShapedText);
 
   // Helper to adjust for synthetic bold and set character-type flags
   // in the shaped text; implementations of ShapeText should call this
@@ -1990,8 +1988,9 @@ class gfxFont {
   template <typename T>
   bool ShapeTextWithoutWordCache(DrawTarget* aDrawTarget, const T* aText,
                                  uint32_t aOffset, uint32_t aLength,
-                                 Script aScript, bool aVertical,
-                                 RoundingFlags aRounding, gfxTextRun* aTextRun);
+                                 Script aScript, nsAtom* aLanguage,
+                                 bool aVertical, RoundingFlags aRounding,
+                                 gfxTextRun* aTextRun);
 
   // Shape a fragment of text (a run that is known to contain only
   // "valid" characters, no newlines/tabs/other control chars).
@@ -2001,8 +2000,8 @@ class gfxFont {
   template <typename T>
   bool ShapeFragmentWithoutWordCache(DrawTarget* aDrawTarget, const T* aText,
                                      uint32_t aOffset, uint32_t aLength,
-                                     Script aScript, bool aVertical,
-                                     RoundingFlags aRounding,
+                                     Script aScript, nsAtom* aLanguage,
+                                     bool aVertical, RoundingFlags aRounding,
                                      gfxTextRun* aTextRun);
 
   void CheckForFeaturesInvolvingSpace();
@@ -2025,21 +2024,24 @@ class gfxFont {
     uint32_t mLength;
     mozilla::gfx::ShapedTextFlags mFlags;
     Script mScript;
+    RefPtr<nsAtom> mLanguage;
     int32_t mAppUnitsPerDevUnit;
     PLDHashNumber mHashKey;
     bool mTextIs8Bit;
     RoundingFlags mRounding;
 
     CacheHashKey(const uint8_t* aText, uint32_t aLength, uint32_t aStringHash,
-                 Script aScriptCode, int32_t aAppUnitsPerDevUnit,
+                 Script aScriptCode, nsAtom* aLanguage,
+                 int32_t aAppUnitsPerDevUnit,
                  mozilla::gfx::ShapedTextFlags aFlags, RoundingFlags aRounding)
         : mLength(aLength),
           mFlags(aFlags),
           mScript(aScriptCode),
+          mLanguage(aLanguage),
           mAppUnitsPerDevUnit(aAppUnitsPerDevUnit),
           mHashKey(aStringHash + static_cast<int32_t>(aScriptCode) +
                    aAppUnitsPerDevUnit * 0x100 + uint16_t(aFlags) * 0x10000 +
-                   int(aRounding)),
+                   int(aRounding) + (aLanguage ? aLanguage->hash() : 0)),
           mTextIs8Bit(true),
           mRounding(aRounding) {
       NS_ASSERTION(aFlags & mozilla::gfx::ShapedTextFlags::TEXT_IS_8BIT,
@@ -2048,11 +2050,13 @@ class gfxFont {
     }
 
     CacheHashKey(const char16_t* aText, uint32_t aLength, uint32_t aStringHash,
-                 Script aScriptCode, int32_t aAppUnitsPerDevUnit,
+                 Script aScriptCode, nsAtom* aLanguage,
+                 int32_t aAppUnitsPerDevUnit,
                  mozilla::gfx::ShapedTextFlags aFlags, RoundingFlags aRounding)
         : mLength(aLength),
           mFlags(aFlags),
           mScript(aScriptCode),
+          mLanguage(aLanguage),
           mAppUnitsPerDevUnit(aAppUnitsPerDevUnit),
           mHashKey(aStringHash + static_cast<int32_t>(aScriptCode) +
                    aAppUnitsPerDevUnit * 0x100 + uint16_t(aFlags) * 0x10000 +
diff --git a/gfx/thebes/gfxGDIFont.cpp b/gfx/thebes/gfxGDIFont.cpp
index 809b91c6ffc9..4d6574cadbbf 100644
--- a/gfx/thebes/gfxGDIFont.cpp
+++ b/gfx/thebes/gfxGDIFont.cpp
@@ -59,7 +59,8 @@ UniquePtr<gfxFont> gfxGDIFont::CopyWithAntialiasOption(
 
 bool gfxGDIFont::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                            uint32_t aOffset, uint32_t aLength, Script aScript,
-                           bool aVertical, RoundingFlags aRounding,
+                           nsAtom* aLanguage, bool aVertical,
+                           RoundingFlags aRounding,
                            gfxShapedText* aShapedText) {
   if (!mIsValid) {
     NS_WARNING("invalid font! expect incorrect text rendering");
@@ -67,7 +68,7 @@ bool gfxGDIFont::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
   }
 
   return gfxFont::ShapeText(aDrawTarget, aText, aOffset, aLength, aScript,
-                            aVertical, aRounding, aShapedText);
+                            aLanguage, aVertical, aRounding, aShapedText);
 }
 
 const gfxFont::Metrics& gfxGDIFont::GetHorizontalMetrics() { return *mMetrics; }
diff --git a/gfx/thebes/gfxGDIFont.h b/gfx/thebes/gfxGDIFont.h
index 0bffb091ef4b..b5ccb8940f23 100644
--- a/gfx/thebes/gfxGDIFont.h
+++ b/gfx/thebes/gfxGDIFont.h
@@ -61,10 +61,9 @@ class gfxGDIFont : public gfxFont {
  protected:
   const Metrics& GetHorizontalMetrics() override;
 
-  /* override to ensure the cairo font is set up properly */
   bool ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                  uint32_t aOffset, uint32_t aLength, Script aScript,
-                 bool aVertical, RoundingFlags aRounding,
+                 nsAtom* aLanguage, bool aVertical, RoundingFlags aRounding,
                  gfxShapedText* aShapedText) override;
 
   void Initialize();  // creates metrics and Cairo fonts
diff --git a/gfx/thebes/gfxGDIFontList.cpp b/gfx/thebes/gfxGDIFontList.cpp
index 89b114d19e2d..b5ff31abd665 100644
--- a/gfx/thebes/gfxGDIFontList.cpp
+++ b/gfx/thebes/gfxGDIFontList.cpp
@@ -826,7 +826,7 @@ bool gfxGDIFontList::FindAndAddFamilies(StyleGenericFontFamily aGeneric,
                                         const nsACString& aFamily,
                                         nsTArray<FamilyAndGeneric>* aOutput,
                                         FindFamiliesFlags aFlags,
-                                        gfxFontStyle* aStyle,
+                                        gfxFontStyle* aStyle, nsAtom* aLanguage,
                                         gfxFloat aDevToCssSize) {
   NS_ConvertUTF8toUTF16 key16(aFamily);
   BuildKeyNameFromFontName(key16);
@@ -842,12 +842,12 @@ bool gfxGDIFontList::FindAndAddFamilies(StyleGenericFontFamily aGeneric,
     return false;
   }
 
-  return gfxPlatformFontList::FindAndAddFamilies(aGeneric, aFamily, aOutput,
-                                                 aFlags, aStyle, aDevToCssSize);
+  return gfxPlatformFontList::FindAndAddFamilies(
+      aGeneric, aFamily, aOutput, aFlags, aStyle, aLanguage, aDevToCssSize);
 }
 
-FontFamily gfxGDIFontList::GetDefaultFontForPlatform(
-    const gfxFontStyle* aStyle) {
+FontFamily gfxGDIFontList::GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                                     nsAtom* aLanguage) {
   FontFamily ff;
 
   // this really shouldn't fail to find a font....
diff --git a/gfx/thebes/gfxGDIFontList.h b/gfx/thebes/gfxGDIFontList.h
index ff015093cf1f..70a2357e173f 100644
--- a/gfx/thebes/gfxGDIFontList.h
+++ b/gfx/thebes/gfxGDIFontList.h
@@ -308,6 +308,7 @@ class gfxGDIFontList final : public gfxPlatformFontList {
                           nsTArray<FamilyAndGeneric>* aOutput,
                           FindFamiliesFlags aFlags,
                           gfxFontStyle* aStyle = nullptr,
+                          nsAtom* aLanguage = nullptr,
                           gfxFloat aDevToCssSize = 1.0) override;
 
   virtual gfxFontEntry* LookupLocalFont(const nsACString& aFontName,
@@ -328,7 +329,8 @@ class gfxGDIFontList final : public gfxPlatformFontList {
                                       FontListSizes* aSizes) const;
 
  protected:
-  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle) override;
+  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                       nsAtom* aLanguage = nullptr) override;
 
  private:
   friend class gfxWindowsPlatform;
diff --git a/gfx/thebes/gfxGraphiteShaper.cpp b/gfx/thebes/gfxGraphiteShaper.cpp
index c5ce613f8f0e..45996fff2dab 100644
--- a/gfx/thebes/gfxGraphiteShaper.cpp
+++ b/gfx/thebes/gfxGraphiteShaper.cpp
@@ -131,7 +131,8 @@ static inline size_t CountUnicodes(const char16_t* aText, uint32_t aLength) {
 bool gfxGraphiteShaper::ShapeText(DrawTarget* aDrawTarget,
                                   const char16_t* aText, uint32_t aOffset,
                                   uint32_t aLength, Script aScript,
-                                  bool aVertical, RoundingFlags aRounding,
+                                  nsAtom* aLanguage, bool aVertical,
+                                  RoundingFlags aRounding,
                                   gfxShapedText* aShapedText) {
   const gfxFontStyle* style = mFont->GetStyle();
   auto t_mGrFace = rlbox::from_opaque(mGrFace);
@@ -191,9 +192,9 @@ bool gfxGraphiteShaper::ShapeText(DrawTarget* aDrawTarget,
     grLang = MakeGraphiteLangTag(style->languageOverride);
   } else if (entry->mLanguageOverride) {
     grLang = MakeGraphiteLangTag(entry->mLanguageOverride);
-  } else if (style->explicitLanguage) {
+  } else if (aLanguage) {
     nsAutoCString langString;
-    style->language->ToUTF8String(langString);
+    aLanguage->ToUTF8String(langString);
     grLang = GetGraphiteTagForLang(langString);
   }
   tainted_gr<gr_feature_val*> grFeatures =
diff --git a/gfx/thebes/gfxGraphiteShaper.h b/gfx/thebes/gfxGraphiteShaper.h
index e2951119dcc7..fc61ac10df38 100644
--- a/gfx/thebes/gfxGraphiteShaper.h
+++ b/gfx/thebes/gfxGraphiteShaper.h
@@ -23,7 +23,7 @@ class gfxGraphiteShaper : public gfxFontShaper {
 
   bool ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                  uint32_t aOffset, uint32_t aLength, Script aScript,
-                 bool aVertical, RoundingFlags aRounding,
+                 nsAtom* aLanguage, bool aVertical, RoundingFlags aRounding,
                  gfxShapedText* aShapedText) override;
 
   static void Shutdown();
diff --git a/gfx/thebes/gfxHarfBuzzShaper.cpp b/gfx/thebes/gfxHarfBuzzShaper.cpp
index ff64c39fd902..8153613896ea 100644
--- a/gfx/thebes/gfxHarfBuzzShaper.cpp
+++ b/gfx/thebes/gfxHarfBuzzShaper.cpp
@@ -1355,7 +1355,8 @@ void gfxHarfBuzzShaper::InitializeVertical() {
 bool gfxHarfBuzzShaper::ShapeText(DrawTarget* aDrawTarget,
                                   const char16_t* aText, uint32_t aOffset,
                                   uint32_t aLength, Script aScript,
-                                  bool aVertical, RoundingFlags aRounding,
+                                  nsAtom* aLanguage, bool aVertical,
+                                  RoundingFlags aRounding,
                                   gfxShapedText* aShapedText) {
   mUseVerticalPresentationForms = false;
 
@@ -1415,9 +1416,9 @@ bool gfxHarfBuzzShaper::ShapeText(DrawTarget* aDrawTarget,
     language = hb_ot_tag_to_language(style->languageOverride);
   } else if (entry->mLanguageOverride) {
     language = hb_ot_tag_to_language(entry->mLanguageOverride);
-  } else if (style->explicitLanguage) {
+  } else if (aLanguage) {
     nsCString langString;
-    style->language->ToUTF8String(langString);
+    aLanguage->ToUTF8String(langString);
     language = hb_language_from_string(langString.get(), langString.Length());
   } else {
     language = hb_ot_tag_to_language(HB_OT_TAG_DEFAULT_LANGUAGE);
diff --git a/gfx/thebes/gfxHarfBuzzShaper.h b/gfx/thebes/gfxHarfBuzzShaper.h
index a5701c8541d9..31c879b052d8 100644
--- a/gfx/thebes/gfxHarfBuzzShaper.h
+++ b/gfx/thebes/gfxHarfBuzzShaper.h
@@ -29,7 +29,7 @@ class gfxHarfBuzzShaper : public gfxFontShaper {
 
   bool ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                  uint32_t aOffset, uint32_t aLength, Script aScript,
-                 bool aVertical, RoundingFlags aRounding,
+                 nsAtom* aLanguage, bool aVertical, RoundingFlags aRounding,
                  gfxShapedText* aShapedText) override;
 
   // get a given font table in harfbuzz blob form
diff --git a/gfx/thebes/gfxMacFont.cpp b/gfx/thebes/gfxMacFont.cpp
index 0e8ff1cf6d5a..8780030a60e1 100644
--- a/gfx/thebes/gfxMacFont.cpp
+++ b/gfx/thebes/gfxMacFont.cpp
@@ -142,7 +142,8 @@ gfxMacFont::~gfxMacFont() {
 
 bool gfxMacFont::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
                            uint32_t aOffset, uint32_t aLength, Script aScript,
-                           bool aVertical, RoundingFlags aRounding,
+                           nsAtom* aLanguage, bool aVertical,
+                           RoundingFlags aRounding,
                            gfxShapedText* aShapedText) {
   if (!mIsValid) {
     NS_WARNING("invalid font! expect incorrect text rendering");
@@ -158,7 +159,7 @@ bool gfxMacFont::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
       mCoreTextShaper = MakeUnique<gfxCoreTextShaper>(this);
     }
     if (mCoreTextShaper->ShapeText(aDrawTarget, aText, aOffset, aLength,
-                                   aScript, aVertical, aRounding,
+                                   aScript, aLanguage, aVertical, aRounding,
                                    aShapedText)) {
       PostShapingFixup(aDrawTarget, aText, aOffset, aLength, aVertical,
                        aShapedText);
@@ -181,7 +182,7 @@ bool gfxMacFont::ShapeText(DrawTarget* aDrawTarget, const char16_t* aText,
   }
 
   return gfxFont::ShapeText(aDrawTarget, aText, aOffset, aLength, aScript,
-                            aVertical, aRounding, aShapedText);
+                            aLanguage, aVertical, aRounding, aShapedText);
 }
 
 gfxFont::RunMetrics gfxMacFont::Measure(const gfxTextRun* aTextRun,
diff --git a/gfx/thebes/gfxMacFont.h b/gfx/thebes/gfxMacFont.h
index 038fd712e665..3d7157b95789 100644
--- a/gfx/thebes/gfxMacFont.h
+++ b/gfx/thebes/gfxMacFont.h
@@ -63,7 +63,7 @@ class gfxMacFont : public gfxFont {
 
   // override to prefer CoreText shaping with fonts that depend on AAT
   bool ShapeText(DrawTarget* aDrawTarget, const char16_t* aText, uint32_t aOffset, uint32_t aLength,
-                 Script aScript, bool aVertical, RoundingFlags aRounding,
+                 Script aScript, nsAtom* aLanguage, bool aVertical, RoundingFlags aRounding,
                  gfxShapedText* aShapedText) override;
 
   void InitMetrics();
diff --git a/gfx/thebes/gfxMacPlatformFontList.h b/gfx/thebes/gfxMacPlatformFontList.h
index e4d9de17edea..302dc937b373 100644
--- a/gfx/thebes/gfxMacPlatformFontList.h
+++ b/gfx/thebes/gfxMacPlatformFontList.h
@@ -146,6 +146,7 @@ class gfxMacPlatformFontList final : public gfxPlatformFontList {
                           nsTArray<FamilyAndGeneric>* aOutput,
                           FindFamiliesFlags aFlags,
                           gfxFontStyle* aStyle = nullptr,
+                          nsAtom* aLanguage = nullptr,
                           gfxFloat aDevToCssSize = 1.0) override;
 
   // lookup the system font for a particular system font type and set
@@ -163,7 +164,8 @@ class gfxMacPlatformFontList final : public gfxPlatformFontList {
   void ReadSystemFontList(nsTArray<FontFamilyListEntry>* aList);
 
  protected:
-  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle) override;
+  FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                       nsAtom* aLanguage = nullptr) override;
 
  private:
   friend class gfxPlatformMac;
diff --git a/gfx/thebes/gfxMacPlatformFontList.mm b/gfx/thebes/gfxMacPlatformFontList.mm
index 912063458a9d..77806543430b 100644
--- a/gfx/thebes/gfxMacPlatformFontList.mm
+++ b/gfx/thebes/gfxMacPlatformFontList.mm
@@ -1215,7 +1215,7 @@ void gfxMacPlatformFontList::InitSystemFontNames() {
   if (mUseSizeSensitiveSystemFont) {
     NSFont* displaySys = [NSFont systemFontOfSize:128.0];
     NSString* displayFamilyName = GetRealFamilyName(displaySys);
-    if ([displayFamilyName isEqualToString: textFamilyName]) {
+    if ([displayFamilyName isEqualToString:textFamilyName]) {
       mUseSizeSensitiveSystemFont = false;
     } else {
       nsCocoaUtils::GetStringForNSString(displayFamilyName, familyName);
@@ -1374,7 +1374,8 @@ gfxFontEntry* gfxMacPlatformFontList::PlatformGlobalFontFallback(const uint32_t
   return fontEntry;
 }
 
-FontFamily gfxMacPlatformFontList::GetDefaultFontForPlatform(const gfxFontStyle* aStyle) {
+FontFamily gfxMacPlatformFontList::GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                                             nsAtom* aLanguage) {
   nsAutoreleasePool localPool;
 
   NSString* defaultFamily = [[NSFont userFontOfSize:aStyle->size] familyName];
@@ -1459,7 +1460,7 @@ bool gfxMacPlatformFontList::FindAndAddFamilies(mozilla::StyleGenericFontFamily
                                                 const nsACString& aFamily,
                                                 nsTArray<FamilyAndGeneric>* aOutput,
                                                 FindFamiliesFlags aFlags, gfxFontStyle* aStyle,
-                                                gfxFloat aDevToCssSize) {
+                                                nsAtom* aLanguage, gfxFloat aDevToCssSize) {
   if (aFamily.EqualsLiteral(kSystemFont_system)) {
     // Search for special system font name, -apple-system. This is not done via
     // the shared fontlist on Catalina or later, because the hidden system font
@@ -1467,12 +1468,13 @@ bool gfxMacPlatformFontList::FindAndAddFamilies(mozilla::StyleGenericFontFamily
     // this family.
     const nsCString& systemFontFamilyName =
         mUseSizeSensitiveSystemFont && aStyle &&
-        (aStyle->size * aDevToCssSize) >= kTextDisplayCrossover
-            ? mSystemDisplayFontFamilyName : mSystemTextFontFamilyName;
+                (aStyle->size * aDevToCssSize) >= kTextDisplayCrossover
+            ? mSystemDisplayFontFamilyName
+            : mSystemTextFontFamilyName;
     if (SharedFontList() && !nsCocoaFeatures::OnCatalinaOrLater()) {
       FindFamiliesFlags flags = aFlags | FindFamiliesFlags::eSearchHiddenFamilies;
-      return gfxPlatformFontList::FindAndAddFamilies(aGeneric, systemFontFamilyName, aOutput,
-                                                     flags, aStyle, aDevToCssSize);
+      return gfxPlatformFontList::FindAndAddFamilies(aGeneric, systemFontFamilyName, aOutput, flags,
+                                                     aStyle, aLanguage, aDevToCssSize);
     } else {
       if (auto* fam = FindSystemFontFamily(systemFontFamilyName)) {
         aOutput->AppendElement(fam);
@@ -1483,7 +1485,7 @@ bool gfxMacPlatformFontList::FindAndAddFamilies(mozilla::StyleGenericFontFamily
   }
 
   return gfxPlatformFontList::FindAndAddFamilies(aGeneric, aFamily, aOutput, aFlags, aStyle,
-                                                 aDevToCssSize);
+                                                 aLanguage, aDevToCssSize);
 }
 
 void gfxMacPlatformFontList::LookupSystemFont(LookAndFeel::FontID aSystemFontID,
diff --git a/gfx/thebes/gfxPlatform.cpp b/gfx/thebes/gfxPlatform.cpp
index f51f578f363c..c650b89ce224 100644
--- a/gfx/thebes/gfxPlatform.cpp
+++ b/gfx/thebes/gfxPlatform.cpp
@@ -1909,10 +1909,12 @@ bool gfxPlatform::IsFontFormatSupported(uint32_t aFormatFlags) {
 
 gfxFontGroup* gfxPlatform::CreateFontGroup(
     const FontFamilyList& aFontFamilyList, const gfxFontStyle* aStyle,
-    gfxTextPerfMetrics* aTextPerf, FontMatchingStats* aFontMatchingStats,
-    gfxUserFontSet* aUserFontSet, gfxFloat aDevToCssSize) const {
-  return new gfxFontGroup(aFontFamilyList, aStyle, aTextPerf,
-                          aFontMatchingStats, aUserFontSet, aDevToCssSize);
+    nsAtom* aLanguage, bool aExplicitLanguage, gfxTextPerfMetrics* aTextPerf,
+    FontMatchingStats* aFontMatchingStats, gfxUserFontSet* aUserFontSet,
+    gfxFloat aDevToCssSize) const {
+  return new gfxFontGroup(aFontFamilyList, aStyle, aLanguage, aExplicitLanguage,
+                          aTextPerf, aFontMatchingStats, aUserFontSet,
+                          aDevToCssSize);
 }
 
 gfxFontEntry* gfxPlatform::LookupLocalFont(const nsACString& aFontName,
diff --git a/gfx/thebes/gfxPlatform.h b/gfx/thebes/gfxPlatform.h
index 5366a6a11f1b..3abf029880df 100644
--- a/gfx/thebes/gfxPlatform.h
+++ b/gfx/thebes/gfxPlatform.h
@@ -393,7 +393,8 @@ class gfxPlatform : public mozilla::layers::MemoryPressureListener {
    * Create a gfxFontGroup based on the given family list and style.
    */
   gfxFontGroup* CreateFontGroup(const mozilla::FontFamilyList& aFontFamilyList,
-                                const gfxFontStyle* aStyle,
+                                const gfxFontStyle* aStyle, nsAtom* aLanguage,
+                                bool aExplicitLanguage,
                                 gfxTextPerfMetrics* aTextPerf,
                                 FontMatchingStats* aFontMatchingStats,
                                 gfxUserFontSet* aUserFontSet,
diff --git a/gfx/thebes/gfxPlatformFontList.cpp b/gfx/thebes/gfxPlatformFontList.cpp
index aa32f9bb30c6..8ece85c44f93 100644
--- a/gfx/thebes/gfxPlatformFontList.cpp
+++ b/gfx/thebes/gfxPlatformFontList.cpp
@@ -1138,7 +1138,7 @@ gfxFontFamily* gfxPlatformFontList::CheckFamily(gfxFontFamily* aFamily) {
 bool gfxPlatformFontList::FindAndAddFamilies(
     StyleGenericFontFamily aGeneric, const nsACString& aFamily,
     nsTArray<FamilyAndGeneric>* aOutput, FindFamiliesFlags aFlags,
-    gfxFontStyle* aStyle, gfxFloat aDevToCssSize) {
+    gfxFontStyle* aStyle, nsAtom* aLanguage, gfxFloat aDevToCssSize) {
   nsAutoCString key;
   GenerateFontListKey(aFamily, key);
 
@@ -1283,13 +1283,13 @@ bool gfxPlatformFontList::FindAndAddFamilies(
 
 fontlist::Family* gfxPlatformFontList::FindSharedFamily(
     const nsACString& aFamily, FindFamiliesFlags aFlags, gfxFontStyle* aStyle,
-    gfxFloat aDevToCss) {
+    nsAtom* aLanguage, gfxFloat aDevToCss) {
   if (!SharedFontList()) {
     return nullptr;
   }
   AutoTArray<FamilyAndGeneric, 1> families;
   if (!FindAndAddFamilies(StyleGenericFontFamily::None, aFamily, &families,
-                          aFlags, aStyle, aDevToCss) ||
+                          aFlags, aStyle, aLanguage, aDevToCss) ||
       !families[0].mFamily.mIsShared) {
     return nullptr;
   }
@@ -1595,12 +1595,9 @@ void gfxPlatformFontList::GetFontFamiliesFromGenericFamilies(
     PrefFontList* aGenericFamilies) {
   // lookup and add platform fonts uniquely
   for (const nsCString& genericFamily : aGenericNameFamilies) {
-    gfxFontStyle style;
-    style.language = aLangGroup;
-    style.systemFont = false;
     AutoTArray<FamilyAndGeneric, 10> families;
     FindAndAddFamilies(aGenericType, genericFamily, &families,
-                       FindFamiliesFlags(0), &style);
+                       FindFamiliesFlags(0), nullptr, aLangGroup);
     for (const FamilyAndGeneric& f : families) {
       if (!aGenericFamilies->Contains(f.mFamily)) {
         aGenericFamilies->AppendElement(f.mFamily);
diff --git a/gfx/thebes/gfxPlatformFontList.h b/gfx/thebes/gfxPlatformFontList.h
index f27378c5f9ac..6e9de61f66b4 100644
--- a/gfx/thebes/gfxPlatformFontList.h
+++ b/gfx/thebes/gfxPlatformFontList.h
@@ -253,6 +253,7 @@ class gfxPlatformFontList : public gfxFontInfoLoader {
                                   nsTArray<FamilyAndGeneric>* aOutput,
                                   FindFamiliesFlags aFlags,
                                   gfxFontStyle* aStyle = nullptr,
+                                  nsAtom* aLanguage = nullptr,
                                   gfxFloat aDevToCssSize = 1.0);
 
   gfxFontEntry* FindFontForFamily(const nsACString& aFamily,
@@ -585,18 +586,21 @@ class gfxPlatformFontList : public gfxFontInfoLoader {
   mozilla::fontlist::Family* FindSharedFamily(
       const nsACString& aFamily,
       FindFamiliesFlags aFlags = FindFamiliesFlags(0),
-      gfxFontStyle* aStyle = nullptr, gfxFloat aDevToCssSize = 1.0);
+      gfxFontStyle* aStyle = nullptr, nsAtom* aLanguage = nullptr,
+      gfxFloat aDevToCssSize = 1.0);
 
   gfxFontFamily* FindUnsharedFamily(
       const nsACString& aFamily,
       FindFamiliesFlags aFlags = FindFamiliesFlags(0),
-      gfxFontStyle* aStyle = nullptr, gfxFloat aDevToCssSize = 1.0) {
+      gfxFontStyle* aStyle = nullptr, nsAtom* aLanguage = nullptr,
+      gfxFloat aDevToCssSize = 1.0) {
     if (SharedFontList()) {
       return nullptr;
     }
     AutoTArray<FamilyAndGeneric, 1> families;
     if (FindAndAddFamilies(mozilla::StyleGenericFontFamily::None, aFamily,
-                           &families, aFlags, aStyle, aDevToCssSize)) {
+                           &families, aFlags, aStyle, aLanguage,
+                           aDevToCssSize)) {
       return families[0].mFamily.mUnshared;
     }
     return nullptr;
@@ -605,13 +609,14 @@ class gfxPlatformFontList : public gfxFontInfoLoader {
   FontFamily FindFamily(const nsACString& aFamily,
                         FindFamiliesFlags aFlags = FindFamiliesFlags(0),
                         gfxFontStyle* aStyle = nullptr,
+                        nsAtom* aLanguage = nullptr,
                         gfxFloat aDevToCssSize = 1.0) {
     if (SharedFontList()) {
       return FontFamily(
-          FindSharedFamily(aFamily, aFlags, aStyle, aDevToCssSize));
+          FindSharedFamily(aFamily, aFlags, aStyle, aLanguage, aDevToCssSize));
     }
     return FontFamily(
-        FindUnsharedFamily(aFamily, aFlags, aStyle, aDevToCssSize));
+        FindUnsharedFamily(aFamily, aFlags, aStyle, aLanguage, aDevToCssSize));
   }
 
   // Lookup family name in global family list without substitutions or
@@ -766,7 +771,8 @@ class gfxPlatformFontList : public gfxFontInfoLoader {
       const FontEntryTable& aTable, mozilla::MallocSizeOf aMallocSizeOf);
 
   // Platform-specific helper for GetDefaultFont(...).
-  virtual FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle) = 0;
+  virtual FontFamily GetDefaultFontForPlatform(const gfxFontStyle* aStyle,
+                                               nsAtom* aLanguage = nullptr) = 0;
 
   // Protects mFontFamilies.
   mozilla::Mutex mFontFamiliesMutex;
diff --git a/gfx/thebes/gfxTextRun.cpp b/gfx/thebes/gfxTextRun.cpp
index e3301e65d3d4..c78febd602d6 100644
--- a/gfx/thebes/gfxTextRun.cpp
+++ b/gfx/thebes/gfxTextRun.cpp
@@ -1546,7 +1546,8 @@ void gfxTextRun::SetSpaceGlyph(gfxFont* aFont, DrawTarget* aDrawTarget,
       aFont->GetRoundOffsetsToPixels(aDrawTarget);
   gfxShapedWord* sw = aFont->GetShapedWord(
       aDrawTarget, &space, 1, gfxShapedWord::HashMix(0, ' '), Script::LATIN,
-      vertical, mAppUnitsPerDevUnit, flags, roundingFlags, nullptr);
+      /* aLanguage = */ nullptr, vertical, mAppUnitsPerDevUnit, flags,
+      roundingFlags, nullptr);
   if (sw) {
     const GlyphRun* prevRun = TrailingGlyphRun();
     bool isCJK = prevRun && prevRun->mFont == aFont &&
@@ -1733,8 +1734,10 @@ void gfxTextRun::Dump(FILE* out) {
 #  undef APPEND_FLAGS
 #  undef APPEND_FLAG
 
-  fprintf(out, "gfxTextRun@%p (length %u) [%s] [%s]\n", this, mLength,
-          flagsString.get(), flags2String.get());
+  nsAutoCString lang;
+  mFontGroup->Language()->ToUTF8String(lang);
+  fprintf(out, "gfxTextRun@%p (length %u) [%s] [%s] [%s]\n", this, mLength,
+          flagsString.get(), flags2String.get(), lang.get());
 
   uint32_t numGlyphRuns;
   const GlyphRun* glyphRuns = GetGlyphRuns(&numGlyphRuns);
@@ -1744,12 +1747,9 @@ void gfxTextRun::Dump(FILE* out) {
     const gfxFontStyle* style = font->GetStyle();
     nsAutoString styleString;
     nsStyleUtil::AppendFontSlantStyle(style->style, styleString);
-    nsAutoCString lang;
-    style->language->ToUTF8String(lang);
-    fprintf(out, "    [%d] offset=%d %s %f/%g/%s/%s\n", i,
+    fprintf(out, "    [%d] offset=%d %s %f/%g/%s\n", i,
             glyphRuns[i].mCharacterOffset, font->GetName().get(), style->size,
-            style->weight.ToFloat(), NS_ConvertUTF16toUTF8(styleString).get(),
-            lang.get());
+            style->weight.ToFloat(), NS_ConvertUTF16toUTF8(styleString).get());
   }
 
   fprintf(out, "  Glyphs:\n");
@@ -1828,12 +1828,14 @@ void gfxTextRun::Dump(FILE* out) {
 #endif
 
 gfxFontGroup::gfxFontGroup(const FontFamilyList& aFontFamilyList,
-                           const gfxFontStyle* aStyle,
+                           const gfxFontStyle* aStyle, nsAtom* aLanguage,
+                           bool aExplicitLanguage,
                            gfxTextPerfMetrics* aTextPerf,
                            FontMatchingStats* aFontMatchingStats,
                            gfxUserFontSet* aUserFontSet, gfxFloat aDevToCssSize)
     : mFamilyList(aFontFamilyList),
       mStyle(*aStyle),
+      mLanguage(aLanguage),
       mUnderlineOffset(UNDERLINE_OFFSET_NOT_SET),
       mHyphenWidth(-1),
       mDevToCssSize(aDevToCssSize),
@@ -1841,9 +1843,10 @@ gfxFontGroup::gfxFontGroup(const FontFamilyList& aFontFamilyList,
       mTextPerf(aTextPerf),
       mFontMatchingStats(aFontMatchingStats),
       mLastPrefLang(eFontPrefLang_Western),
-      mPageLang(gfxPlatformFontList::GetFontPrefLangFor(aStyle->language)),
+      mPageLang(gfxPlatformFontList::GetFontPrefLangFor(aLanguage)),
       mLastPrefFirstFont(false),
-      mSkipDrawing(false) {
+      mSkipDrawing(false),
+      mExplicitLanguage(aExplicitLanguage) {
   // We don't use SetUserFontSet() here, as we want to unconditionally call
   // BuildFontList() rather than only do UpdateUserFonts() if it changed.
   mCurrGeneration = GetGeneration();
@@ -1869,7 +1872,7 @@ void gfxFontGroup::BuildFontList() {
         MOZ_ASSERT_UNREACHABLE("broken FontFamilyName, no atom!");
       }
     } else {
-      pfl->AddGenericFonts(name.mGeneric, mStyle.language, fonts);
+      pfl->AddGenericFonts(name.mGeneric, mLanguage, fonts);
       if (mTextPerf) {
         mTextPerf->current.genericLookups++;
       }
@@ -1913,8 +1916,7 @@ void gfxFontGroup::BuildFontList() {
   // if necessary, append default generic onto the end
   if (mFamilyList.GetDefaultFontType() != StyleGenericFontFamily::None &&
       !mFamilyList.HasDefaultGeneric()) {
-    pfl->AddGenericFonts(mFamilyList.GetDefaultFontType(), mStyle.language,
-                         fonts);
+    pfl->AddGenericFonts(mFamilyList.GetDefaultFontType(), mLanguage, fonts);
     if (mTextPerf) {
       mTextPerf->current.genericLookups++;
     }
@@ -1953,7 +1955,7 @@ void gfxFontGroup::AddPlatformFont(const nsACString& aName, bool aQuotedName,
       StyleGenericFontFamily::None, aName, &aFamilyList,
       aQuotedName ? gfxPlatformFontList::FindFamiliesFlags::eQuotedFamilyName
                   : gfxPlatformFontList::FindFamiliesFlags(0),
-      &mStyle, mDevToCssSize);
+      &mStyle, mLanguage.get(), mDevToCssSize);
 }
 
 void gfxFontGroup::AddFamilyToFontList(gfxFontFamily* aFamily,
@@ -2541,7 +2543,7 @@ void gfxFontGroup::InitTextRun(DrawTarget* aDrawTarget, gfxTextRun* aTextRun,
     if (sizeof(T) == sizeof(uint8_t) && !transformedString) {
       if (MOZ_UNLIKELY(MOZ_LOG_TEST(log, LogLevel::Warning))) {
         nsAutoCString lang;
-        mStyle.language->ToUTF8String(lang);
+        mLanguage->ToUTF8String(lang);
         nsAutoCString families;
         mFamilyList.ToString(families);
         nsAutoCString str((const char*)aString, aLength);
@@ -2588,7 +2590,7 @@ void gfxFontGroup::InitTextRun(DrawTarget* aDrawTarget, gfxTextRun* aTextRun,
       while (scriptRuns.Next(runStart, runLimit, runScript)) {
         if (MOZ_UNLIKELY(MOZ_LOG_TEST(log, LogLevel::Warning))) {
           nsAutoCString lang;
-          mStyle.language->ToUTF8String(lang);
+          mLanguage->ToUTF8String(lang);
           nsAutoCString families;
           mFamilyList.ToString(families);
           nsAutoString styleString;
@@ -2708,7 +2710,7 @@ void gfxFontGroup::InitScriptRun(DrawTarget* aDrawTarget, gfxTextRun* aTextRun,
                             (matchedLength > 0), range.orientation, isCJK);
       if (!matchedFont->SplitAndInitTextRun(
               aDrawTarget, aTextRun, aString + runStart, aOffset + runStart,
-              matchedLength, aRunScript, range.orientation)) {
+              matchedLength, aRunScript, mLanguage, range.orientation)) {
         // glyph layout failed! treat as missing glyphs
         matchedFont = nullptr;
       }
@@ -2743,7 +2745,7 @@ void gfxFontGroup::InitScriptRun(DrawTarget* aDrawTarget, gfxTextRun* aTextRun,
                               (matchedLength > 0), range.orientation, isCJK);
         if (!subSuperFont->SplitAndInitTextRun(
                 aDrawTarget, aTextRun, aString + runStart, aOffset + runStart,
-                matchedLength, aRunScript, range.orientation)) {
+                matchedLength, aRunScript, mLanguage, range.orientation)) {
           // glyph layout failed! treat as missing glyphs
           matchedFont = nullptr;
         }
@@ -2755,7 +2757,8 @@ void gfxFontGroup::InitScriptRun(DrawTarget* aDrawTarget, gfxTextRun* aTextRun,
         if (!matchedFont->InitFakeSmallCapsRun(
                 aDrawTarget, aTextRun, aString + runStart, aOffset + runStart,
                 matchedLength, range.matchType, range.orientation, aRunScript,
-                syntheticLower, syntheticUpper)) {
+                mExplicitLanguage ? mLanguage.get() : nullptr, syntheticLower,
+                syntheticUpper)) {
           matchedFont = nullptr;
         }
       } else {
@@ -2777,7 +2780,7 @@ void gfxFontGroup::InitScriptRun(DrawTarget* aDrawTarget, gfxTextRun* aTextRun,
                               (matchedLength > 0), range.orientation, isCJK);
         if (!matchedFont->SplitAndInitTextRun(
                 aDrawTarget, aTextRun, aString + runStart, aOffset + runStart,
-                matchedLength, aRunScript, range.orientation)) {
+                matchedLength, aRunScript, mLanguage, range.orientation)) {
           // glyph layout failed! treat as missing glyphs
           matchedFont = nullptr;
         }
@@ -3522,7 +3525,7 @@ void gfxFontGroup::ComputeRanges(nsTArray<TextRange>& aRanges, const T* aString,
 
   if (MOZ_UNLIKELY(MOZ_LOG_TEST(log, LogLevel::Debug))) {
     nsAutoCString lang;
-    mStyle.language->ToUTF8String(lang);
+    mLanguage->ToUTF8String(lang);
     nsAutoCString families;
     mFamilyList.ToString(families);
 
diff --git a/gfx/thebes/gfxTextRun.h b/gfx/thebes/gfxTextRun.h
index c8c702a01c0c..e5720b21e6f1 100644
--- a/gfx/thebes/gfxTextRun.h
+++ b/gfx/thebes/gfxTextRun.h
@@ -932,7 +932,8 @@ class gfxFontGroup final : public gfxTextRunFactory {
   Shutdown();  // platform must call this to release the languageAtomService
 
   gfxFontGroup(const mozilla::FontFamilyList& aFontFamilyList,
-               const gfxFontStyle* aStyle, gfxTextPerfMetrics* aTextPerf,
+               const gfxFontStyle* aStyle, nsAtom* aLanguage,
+               bool aExplicitLanguage, gfxTextPerfMetrics* aTextPerf,
                FontMatchingStats* aFontMatchingStats,
                gfxUserFontSet* aUserFontSet, gfxFloat aDevToCssSize);
 
@@ -1092,6 +1093,8 @@ class gfxFontGroup final : public gfxTextRunFactory {
     }
   }
 
+  nsAtom* Language() const { return mLanguage.get(); }
+
  protected:
   friend class mozilla::PostTraversalTask;
 
@@ -1377,6 +1380,8 @@ class gfxFontGroup final : public gfxTextRunFactory {
   RefPtr<gfxFont> mDefaultFont;
   gfxFontStyle mStyle;
 
+  RefPtr<nsAtom> mLanguage;
+
   gfxFloat mUnderlineOffset;
   gfxFloat mHyphenWidth;
   gfxFloat mDevToCssSize;
@@ -1405,6 +1410,8 @@ class gfxFontGroup final : public gfxTextRunFactory {
                       // download to complete (or fallback
                       // timer to fire)
 
+  bool mExplicitLanguage;  // Does mLanguage come from an explicit attribute?
+
   uint32_t mFontListGeneration = 0;  // platform font list generation for this
                                      // fontgroup