I wasted a lot of time trying to figure out how to add the "no" (Norway-Norwegian with dead keys) keyboard layout my list of keyboard layouts, since I couldn't find it in the list under the "Norwegian" category. I found Norwegian without dead keys, Mac-style with and without dead keys, Colemac, Dvorak, but no Norwegian with dead keys. But I knew it was there, since it was the system standard and worked if I simply chose "use system standard" without any other layouts available for switching.

Finally, I noticed I could click the category itself. This did not make sense to me before, since the other layouts are not actually sub-variants of Norwegian (e.g. Northern Saami is not even in the same language family …). 

I think the UI would be a lot less confusing if standard Norwegian got its own line in the sub-category, instead of the user having to discover that you can click the category as well as entries within it.