Clean bookworm, freshly installed today.

The locales generated via locale-gen show up in Gnome Settings > Region
& Language.  However, selecting them does nothing; the Gnome UI remains
stuck in English.

The locales were generated post-install via /etc/locale.gen /
dpkg-reconfigure locales, and work fine for other applications via
setting LANG/LC_ALL.

The problem may be related to a LANGUAGE=en_US:en variable that appears
when I log in via GDM.  It does not appear if I log in via console.

Some things I tried which didn't help:
 - gsettings set org.gnome.system.locale region (it was empty)
 - editing /var/lib/AccountsService/user/myuser (it was correct)
 - creating a ~/.config/locale.conf
 - regenerating locales via locale-gen
 - regenerating locales via dpkg-reconfigure locales
 - removing English locales from the system, and regenerating them
 - setting the default system language to something other than English
 - setting the "Region & Language" option to English then back to
   another language

No matter what I do, Gnome remains in English.

(I'm sorry if this isn't the right package to report, I couldn't find
previous reports from web searches.)