Comment 8 for bug 2035212

The description looks right to me now.

The thing is that the regional formats value you set is *also* represented by a line in a user file in the /var/lib/AccountsService/users directory. There is quite some code which tries to keep that line in sync with ~/.pam_environment, and by changing those variables in ~/.pam_environment only they got out of sync. :/

If you want to use a script in connection with preparing a distro, one way is to change it in both places.

Or probably better: Let the script edit only /etc/default/locale to your liking and don't create ~/.pam_environment in advance.

A few years ago I figured out a terminal command to change the user's regional format value the 'right' way:

https://askubuntu.com/a/754519

It's pretty long...