I can’t find this question back in the forum, but it’s also hard to believe that I ask this as first 
Is it an idea to have language specific sub-fora (or category)? Where we can use the community in our own native language and also discuse and share country specific items?
The general forum is only available in English. You can use Private Message to converse in your native language to other users.
@Brucanna
How can one see what the nationality/native language of the forum users is?
Only by the contents of their posts.
Most topics are generic so they are applicable to all nationalities / users, however country related topics - “2a” in dutch tax-report - stand out due to the specific details in the topic.
Some users include nationality in their public profiles, but most do not.