Thanks again for your suggestions, Gunnar. I copied your commands directly from here to the terminal, so it is not a typo.
Strangely, setting env LANG with firefox or thunderbird actually worked on the last three Ubuntu versions, even though it may be incorrect to run it this way. I was able to run an English instance of Thunderbird, for example, by using env LANG.
Thanks again for your suggestions, Gunnar. I copied your commands directly from here to the terminal, so it is not a typo.
Strangely, setting env LANG with firefox or thunderbird actually worked on the last three Ubuntu versions, even though it may be incorrect to run it this way. I was able to run an English instance of Thunderbird, for example, by using env LANG.
I have opened a separate bug report here: https:/ /bugs.launchpad .net/ubuntu/ +source/ gdm/+bug/ 792735 and supplied more information to track down the problem. Any suggestions would be welcome!