I've got no hints on the subject of Ctrl+Space (I never DiD figure out where in the whole xkb scheme that Ctrl+Space combo gets set/activated, but the keyboard map file mentions it's hardcoded into hildon, whatever that means).

However, in the meantime, I can offer an alternative, in the form of http://wiki.maemo.org/remapping_keyboard , where I happened to make some detailed edits in the past on how to not only remap the keyboard, but also how to remap it with multiple layouts (and by extension multiple possible languages - more than just 2 if so desired).