I experienced a bug in the Windows Phone 8 Store : I localized my app titles with the AppResLib.dll (& mui) and the tiles title were ok in the phone but the WP8 Store shown only the neutral language title. (on WP7 Store only, it looks ok!)
In the WMAppManifest.xml (WP8) or in the project settings (WP7), you have to uncheck generic language codes (as “fr”,”it”,”de”) and check all the sub-language codes like “fr-FR”,”fr-BE”,”it-IT”, etc. If you check both generic and sub-languages, this will not working.
For the moment : don’t ever use the generic language codes (if you used them in your old WP7 app, this will appears Ok on WP7 Store but incorrectly on WP8 Store)
That’s all and this works !