Bug 1607111 - Use BCP47 lang tags for negotiation in content process. r=jfkthame

Differential Revision: https://phabricator.services.mozilla.com/D60089

--HG--
extra : moz-landing-system : lando

dom/ipc/ContentParent.cpp

@@ -2523,7 +2523,7 @@ bool ContentParent::InitInternal(ProcessPriority aInitialPriority) {
 
   spellChecker->GetDictionaryList(&xpcomInit.dictionaries());
 
-  LocaleService::GetInstance()->GetAppLocalesAsLangTags(xpcomInit.appLocales());
+  LocaleService::GetInstance()->GetAppLocalesAsBCP47(xpcomInit.appLocales());
   LocaleService::GetInstance()->GetRequestedLocales(
       xpcomInit.requestedLocales());