What is the Hunnish language look like?
...Royal Swedish? With no difference from Icelandic, or did it just take over Icelandic?
TTL Icelandic is almost as OTL Icelandic. Royal swedish is language of the swedish royal court, developed from Old Swedish in few different ways to colloquial language of Sweden.
Ah...so what about the other Norse-derived languages? Are they all gone, or are they considered dialectic variantions, or are they accepted as provincial languages, or something else?
These language are accepted by state policy and have regional status (as Kashubian in polish, but are undangered and widely used).
Russian and Polish existing is pretty weird.