I assumed you'd like to do the same with `nb_NO` and `nn_NO` as you already do with `en_GB`, `zh_CN` and `zh_TW`.
`nb_NO` and `nn_NO` are quite similar, so it's probably OK to have `nn_NO` apply if system language/culture is anything `NO` and no `nb_NO` yet exist.
But I'd rather have it default to english when my closest language is ~17% complete ( https://www.geany.org/contribute/translation/statistics/ ). Maybe some threshold should be set for when to use translation?
About contributing with translations: Would be great with a non-technical way to do it, maybe some crowdsourcing in browser solution can be looked into?