Language fallbacks

I hadn't thought about there being no other fallbacks. Norwegians understand (written) Swedish and Danish just fine, but in my mind I think it makes more sense to have missing translations just fall back to English, as that signifies that there is no translation, while on the other hand if they were to fall back to Swedish, I can imagine some complaints and users questioning if there's a bug that makes stuff appear in Swedish rather than Norwegian (since it's not obvious why it is in Swedish). nb and nn should have reciprocal fallback though, I can't imagine any complaints about that.

True, let's do at least nb<->nn.