Some recent update has caused my Thunderbird (14.0 on Ubuntu 12.04) to revert to an English-language user interface. It used to be German before.
My system is completely in German. German language support is fully installed in System Settings.
thunderbird-locale-de is installed as well. I even tried to remove and reinstall this package, without any visible change.
I also tried resetting
de-DE via Thunderbird's own configuration editor. No change as well.
How do I get my German interface back?