How to change keyboard layout used during boot-time in Debian

Let say you have an encrypted partition unto which you ought to enter a passphrase during bootup. This can cause some trouble if your password uses extended characters such as à é è or any other - which is an amazing idea by the way.

The keyboard locale during system boot is different than the one used when booted in the Debian OS GUI.

To edit the bootup language, edit /etc/default/keyboard

/etc/default/keyboard:
XKBLAYOUT="ca"
XKBVARIANT="fr"