Comment 6 for bug 1916935

FYI - This happens only to a login shell

$ ssh ubuntu@192.168.122.177 "env | grep LC_NUM";
LC_NUMERIC=de_DE.UTF-8
ssh ubuntu@192.168.122.177 -t 'bash -l -c "env | grep LC_NUM"'
LC_NUMERIC=C.UTF-8

And while downgrading I saw the suspicious
/etc/profile.d/01-locale-fix.sh: line 2: /usr/bin/locale-check: No such file or directory

$ cat /etc/profile.d/01-locale-fix.sh
# Make sure the locale variables are set to valid values.
eval $(/usr/bin/locale-check C.UTF-8)

And indeed on "release" Bionic that binary used there isn't present.

I checked where it came from:
$ dpkg -S /usr/bin/locale-check
base-files: /usr/bin/locale-check

So it seems this check was always meant to work, but on bionic-release calls a file that isn't present and therefore is not in effect to "fixup" the locales on a login shell.

Now that I know that I was able to swicth between old/new behavior by switching "just" base files 10.1ubuntu2 <-> 10.1ubuntu2.10.

That change was introduced back in 2018 via bug 1134036 as far as I found.

I'm not sure what to do, this is "longer in the field with the new behavior" and not new at all.
So changing it either way might regress people.
But in any case we can re-target this bug against base-files for re-consideration now that we know all that.