diff --git a/intl/locale/idl/nsILanguageAtom.idl b/intl/locale/idl/nsILanguageAtom.idl
new file mode 100644
index 00000000000..4919d2ca132
--- /dev/null
+++ b/intl/locale/idl/nsILanguageAtom.idl
@@ -0,0 +1,47 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * The contents of this file are subject to the Mozilla Public
+ * License Version 1.1 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of
+ * the License at http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS
+ * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
+ * implied. See the License for the specific language governing
+ * rights and limitations under the License.
+ *
+ * The Original Code is Mozilla Communicator.
+ *
+ * The Initial Developer of the Original Code is Netscape Communications
+ * Corp.  Portions created by Netscape are Copyright (C) 2000 Netscape
+ * Communications Corp.  All Rights Reserved.
+ *
+ * Contributor(s):
+ *   Erik van der Poel
+ */
+
+#include "nsISupports.idl"
+#include "nsIAtom.idl"
+
+/*
+ * The nsILanguageAtom interface encapsulates a language code (as used in
+ * HTML LANG attributes, for example). This interface also provides access
+ * to the corresponding "language group" atom, to be used in the font
+ * engine with preferences, for example.
+ *
+ * The nsILanguageAtom interface is similar to nsIAtom, in the sense that
+ * one can compare 2 pointers for equality. The nsILanguageAtomService
+ * creates nsILanguageAtoms by first lower-casing the language (since it's
+ * case-insensitive according to RFC 1766), and then looking up that
+ * language in a set of existing nsILanguageAtom objects. If it already
+ * exists, that object is returned. If not, a new one is created and added
+ * to the set for future retrieval.
+ */
+[scriptable, uuid(a6cf911e-15b3-11d2-932e-00805f8add32)]
+interface nsILanguageAtom : nsISupports
+{
+  readonly attribute wstring language;
+  readonly attribute nsIAtom languageGroup;
+
+  boolean LanguageIs(in wstring aLanguage);
+};
diff --git a/intl/locale/idl/nsILanguageAtomService.idl b/intl/locale/idl/nsILanguageAtomService.idl
new file mode 100644
index 00000000000..bffc0183754
--- /dev/null
+++ b/intl/locale/idl/nsILanguageAtomService.idl
@@ -0,0 +1,47 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * The contents of this file are subject to the Mozilla Public
+ * License Version 1.1 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of
+ * the License at http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS
+ * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
+ * implied. See the License for the specific language governing
+ * rights and limitations under the License.
+ *
+ * The Original Code is Mozilla Communicator.
+ *
+ * The Initial Developer of the Original Code is Netscape Communications
+ * Corp.  Portions created by Netscape are Copyright (C) 2000 Netscape
+ * Communications Corp.  All Rights Reserved.
+ *
+ * Contributor(s):
+ *   Erik van der Poel
+ */
+
+#include "nsISupports.idl"
+#include "nsILanguageAtom.idl"
+
+/*
+ * The nsILanguageAtomService creates nsILanguageAtoms based on a given
+ * language or charset. See the nsILanguageAtom documentation for further
+ * info. When a charset is looked up, the resulting nsILanguageAtom does
+ * not contain a language (since the language cannot be known in the general
+ * case), but the language group is set appropriately.
+ */
+[scriptable, uuid(a6cf911f-15b3-11d2-932e-00805f8add32)]
+interface nsILanguageAtomService : nsISupports
+{
+  nsILanguageAtom LookupLanguage(in wstring aLanguage);
+  nsILanguageAtom LookupCharSet(in wstring aCharSet);
+};
+
+%{C++
+
+#define NS_LANGUAGEATOMSERVICE_CID \
+  {0xa6cf9120, 0x15b3, 0x11d2, {0x93, 0x2e, 0x00, 0x80, 0x5f, 0x8a, 0xdd, 0x32}}
+#define NS_LANGUAGEATOMSERVICE_PROGID \
+  "component://netscape/intl/nslanguageatomservice"
+
+%}