Update:Extension Localization Update Issues

Some random notes on extension localization update; shaver made me do it.

• Locale packs for extensions should exist
  • Probably should be marked as depending on the extension to be localized, or something
• On extension update, if a corresponding locale update is not available, indicate this to the user.
• Use the localized strings where the strings exist, and fallback only if it does not
  • If the only unlocalized string is obscure, using a partially localized version is much more preferable to completely not localized
• Fallback should be according to the user's locale prefs (or region or something), and to the untranslated version (as came in the extension, not necessarily en-US) if not possible