There are quite a few “X·ish language” sites online by now, and they seem to be really useful for learners to ask native speakers.
Each of the nordic countries is probably too small to have an own SE. (E.g. Norwegian seems to have been deleted.) But the Danish, Norwegian and Swedish languages are pretty similar, and so I think a shared site for the three of them could get enough users that might still be able to understand many of the questions.
Unfortunately, you're not really going to be able to answer that question here. The community you should ask is the people who would actually build and use this site. That community is not here, and Area 51 cannot find that community for you.
The proposal process assumes (and now requires) that you have an avid community organized and ready to build a proposal before you submit it. So if you know of a community encompassing those subjects needing a Q&A, then I would ask them if they'd be interested in building such a site.
If they've been able to make that combination work elsewhere, it would likely work here also. Otherwise, you might find that folks are more apt to support a Q&A focused on their language specifically. But you should see if those communities are interested before submitting a proposal.
Minimum number of people for a successful proposal
Good luck!
