@tournesol back in the day it was done with 'loadkeys', eg 'loadkeys es' for Spanish. I believe that still works? I don't have a nearby tty right now to test. Needs to be added to .bashrc (or the rcfile of your shell) for subsequent reboots.
@CouldBeMathijs I did all the keyboard-configuration command I could find and think I modified the intiramfs, don’t really which one did the trick (but yeah, I rebooted for every changes)