When I used Ubuntu 10.04, I can choose session language at login, see
Now I upgraded to 12.04 (I remove unity and use GDM instead), I can't choose the language anymore, see
How to fix this, please.
If you use GDM, you can't fix it, since that feature was removed.
If you use LightDM, and install lightdm-gtk-greeter, you can still set the language at login. Open Language Support, click the Help button and select "Alternative language settings" for a short instruction.