I don't have a solution for gdm, I don't use DMs for precisely the problems like yours.
I changed my boot procedure, i use 'startx' and if i wanna change my window manager, i do it from the .xinitrc
Edit /etc/inittab as ROOT, and change the 'default run level' to 3 and reboot.
# Default runlevel. (Do not set to 0 or 6 !)
When you come back login with your user_name (Enter)
$ startx (Enter) and you're in like Fynn, it never fails.
Hopefully the lang will be like the rest of the system.
Otherwise, never mind my ramblings...