Internet Explorer has more explicit language names in Windows Vista

In Windows XP, Internet Explorer only provided partial tags for some languages.  French (France) was "fr" and Japanese was "ja", yet English was "en-US".

In Windows Vista, IE7 is now using full locale names for the language, so HTTP Accept Language should now provide more complete information.  (ie: ja-JP for Japanese, fr-FR for French (France)).

IE7 will also enumerate all of the system locales in the Language Preferences dialog, so custom locales / cultures such as haw-US, fj-FJ or even tlh-US would be listed for the user to select.  Of course the user can still enter their own language tag if the desired locale isn't on the list.