Comment 6 for bug 1778225

/etc/default/locale and ~/.pam_environment are the only files which are written to via the GUIs, and both of them look normal to me. The locale output, however, is not consistent with those files. With that ~/.pam_environment file it ought to look like this:

LANG=en_US.UTF-8
LANGUAGE=en
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=de_DE.UTF-8
LC_TIME=de_DE.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=de_DE.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=de_DE.UTF-8
LC_NAME=de_DE.UTF-8
LC_ADDRESS=de_DE.UTF-8
LC_TELEPHONE=de_DE.UTF-8
LC_MEASUREMENT=de_DE.UTF-8
LC_IDENTIFICATION=de_DE.UTF-8
LC_ALL=

So the variables set by ~/.pam_environment seem to be overridden somehow by settings somewhere else. Actually, I see in the attached ProcEnviron.txt file that every single locale category has been set explicitly (to German) - also variables which are not set by any of those two files such as LC_CTYPE and LC_MESSAGES.

More questions:

Are you possibly accessing the PC remotely from some other machine via SSH or something?

What's the output from these commands:

  dpkg-query -W gdm3

  cat /etc/environment