Something funky with locale indeed, I have en_US.UTF-8 & nl_NL.UTF-8 installed.
For some reason after glibc update this happens:
Upgrading glibc (2.32-5 -> 2.33-3)...
Generating locales...
de_DE.UTF-8... done
en_US.UTF-8... done
Generation complete.
Upgrading gcc-libs (10.2.0-4 -> 10.2.0-6)...
Then further down:
-> Running build hook: [keymap]
/etc/locale.conf: line 2: warning: setlocale: LC_NUMERIC: cannot change locale (nl_NL.UTF-8)
/etc/locale.conf: line 3: warning: setlocale: LC_TIME: cannot change locale (nl_NL.UTF-8)
-> Running build hook: [plymouth]
$ cat /etc/locale.conf
LANG=en_US.utf8
LC_NUMERIC=nl_NL.UTF-8
LC_TIME=nl_NL.UTF-8
LC_COLLATE=C
LC_MONETARY=nl_NL.UTF-8
LC_PAPER=nl_NL.UTF-8
LC_MEASUREMENT=nl_NL.UTF-8
changing de_DE.UTF-8 to #de_DE.UTF-8 and #nl_NL.UTF-8 to nl_NL.UTF-8 in /etc/locale.gen & running $ sudo locale-gen solves this issue.
This seems wrong tho:
$ cat /etc/locale.conf
LANG=en_US.utf8