I have found that Stack Exchange, Yahoo Answers, Zhihu and other sites allow you to immerse yourself in major languages by asking and answering questions on multilingual pages. Are there any such online forums meant for native speakers of Icelandic, Norwegian, Swedish, Danish, Dutch or Afrikaans?
I follow sparsely and comment even more sparsely on the Swedish roleplaying forum at http://www.rollspel.nu/forum
Some newspapers or public broadcasting companies have open comments under some or all of their stories; I read https://www.universitetsavisa.no/ (in Norwegian) which has such, though often there are not that many comments.
It is also very easy to find Facebook groups about whatever in at least the Scandinavian languages, if you are up to using Facebook.
In general, I think the problem is the embarrassment of riches. Choose something subject that interests you, search for [subject name in language of choice] [language name in language of choice] [forum] and variations thereof. Many forums have unfortunately moved to Facebook, but you can always make a Facebook profile with a made-up name, no picture, and invite no friends, and use it for your discussion needs.
The internal Facebook search might also find something, if you search for [subject matter in language of choice], perhaps with the name of the language if the name of the subject matter is similar in several languages. Look for groups.