Comment 9 for bug 79589

Ok, after some checks I found the problem.

With the language pack released on September, we shipped some .po files that shouldn't be there. We fixed that problem and with latest language pack, we stopped shipping those .po files but the way our .deb packages work produced that you lose all those translations.

Martin Pitt will prepare new packages that will fix this problem next week, once he's back from current Ubuntu sprint.

In the mean time, as a fast workaround, you could reinstall latest -base language packs and then, reinstall latest -updates ones. That should restore the translations.