This is a little trick I've found out myself (I was lucky) which solves the annoying problem which prevent you from switching between multiple keyboard layouts in GNOME 2.12.

Click on the keyboard indicator

get to Layout option/ Group shift Lock behaviour/

select "CTRL+SHIFT change group".

Close the window

Press CTRL+SHIFT

Now it should work and you should also be able to switch between the layouts with a mouse click.

Enjoy!

Alberto