All the Scandinavian languages can be read by speakers of the other Scandinavian languages, somewhat accuately, in written form, given enough time, cursing and crying is invested into doing it. Icelandic and Faraoese are quite different from the others, but they're not THAT hard to understand when written down.

Speakers of Danish, Norwegian and Swedish can usually talk to eachother without major issues although the kids seem to be preferring to speak English nowadays.

Spoken Icelandic or Faraoese on the other hand? I usually manage to get a single word or phrase. The rest is gibberish.