While looking for my problem of Keyboad layout: In 13.10, modified symbols do not apply, I noticed that gnome-control-center region layouts has a list of keyboard layouts that is not directly related to the ones found in /usr/share/X11/xkb/symbols. For example, on my German machine it lists ‘Englisch (Colemak)’ and ‘English (Britisch, Colemak)’ as keyboard layouts, both are not found in the original files, but obviously translations.

So, my question is: Where does gnome-control-center get its list of keyboard layouts from? Can it be extended?