Et bah si ca ce n'est pas une réponse rapide et efficace !
Voici le contenu original du fichier /etc/X11/xorg.conf.d/00-system-setup-keyboard.conf
# This file is autogenerated by system-setup-keyboard. Any
# modifications will be lost.
Section "InputClass"
Identifier "system-setup-keyboard"
MatchIsKeyboard "on"
Option "XkbModel" "pc105+inet"
Option "XkbLayout" "us"
# Option "XkbVariant" "(null)"
Option "XkbOptions" "terminate:ctrl_alt_bksp,"
EndSection
Je me suis rapidement attelé à modifier la section
Option "XkbLayout" "us" en
Option "XkbLayout" "fr" ... Et voilà !
Merci VINDICATORs !