“to speak Finnish? Or Icelandic, a mildly related language?”
Finnish is very different from Scandinavian languages - Hungarian is its closest relative. Like the Hungarians (Huns), Finnish people came from the steppes of Asia.
Finland was ruled by the Swedish Empire for a couple of hundred years, and adopted a lot of Scandinavian cultural traits.
I have heard that Finnish is one of the most complicated languages in Europe. Refugees from places like Syria might consider it torture if they have to learn the language.
Finns are meaner
than
norse
Most of the Finnish nobility spoke Swedish almost exclusively.
Even Carl Mannerheim, as a Finn serving in the Russian Imperial Army, spoke little Finnish before the socialists took over Russia. And he is still considered the greatest Finn of all time.