It seems to be rather difficult to change the default keyboard layout used for the lightdm login screen. The following solution worked for me:
- adding the following block of code at the end of
/etc/X11/xorg.conf - (adapt country-code
"ch"in line 3):
Section "InputClass"
Identifier "evdev keyboard catchall"
Option "XkbLayout" "ch"
MatchIsKeyboard "on"
MatchDevicePath "/dev/input/event*"
Driver "evdev"
EndSection