My standard language for Firefox and Thunderbird is Dutch. When I use the terminal to open firefox or thunderbird with the -ProfileManager option, the resulting ProfileManager is in English. How can I change the language to Dutch in the ProfileManager?
You can download a fully localized version of Firefox here:
and then extract that in e.g.
Then, create a directory
Starting from the next time you log in, all invocations of "firefox" (including through the system menus) should invoke your own localized version of Firefox instead of the Ubuntu-maintained version.
(This is what I do, because I'm using a nightly build of Firefox instead of the Ubuntu-maintained version.)