Sorry for spamming you.
The language-tab in abbout:addons appears after making the symlink and the installed language packs are shown in thunderbird.
But all the Menus and buttons (complete ui) is still in english. Maybe i get it wrong, and the language pack is not for UI translations, but only for dictionaries?
If they are only for dictionaries: Do i have to report a new bug concerning the missing translation of the user interface?