Locale settings for specific app-vm (Thunderbird)

I have my template settings as generic as possible, which includes locale settings. This is C.UTF8, i.e. US.
Unfortunately, Thunderbird seems to take its date format from the /etc/locale.config file, which is taken from the template.
The US date convention that comes with “C” is - for me - deeply confusing. I need emails to be listed in a “dd-mm-yyyy” format.
Is there a workaround without changing the template?
PS, my preference is not to make another standalone (trying to keep overheads down).

I did not test this, but would setting it in /rw/config/rc.local via localectl work? This file is persistent (that is, it is not erased if you reboot the qube).

Yup, that worked great. Thanks.

(for others: the how-to given in /rw/config/rc.local is a very good guide.)