I realized my problem: while installing ubuntu, I didn't have an internet connection to load the german language packages, because my dsl-connection was not configured. As I read the bug description again, I went to System - Administration - Language Support and installed the missing language packs. Now everything is ok.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/534417 Title: Thunderbird: localization not installed automatically -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs