Insular Scandinavian and Continental Scandinavian?

..it by began eigth century?
there were ax boat people long before. (the Map by Max Naylor).

I have a few comments.
The Foreign Service Institute has listed the time periods, what you need to learn a specific language as an English speaker.
No matter that this ranking only shows the view of the Foreign Service Institute and some language students or experts may disagree with the ranking, it seems plausible.
Perhaps, there is no better than this one, I think so.

if languages ranked as difficult, sure, it does not mean that they are impossible to learn and maybe it is not hard for you at all.
Nothing can stop you from learning a language, if you love it.
It just goes in accordance with linguistics rules by every language. But he who´s loving, will be learning there.

Förresten,
The Norwegian language, the Icelandic Language, the Danish language, The Finland´s Swedish and the Swedish language self .. all are descendents of the Old Norse language, which was spoken by Germanic people in the Viking Era, mostly living in the Scandinavian area.
In more recent years, linguists have theorized that there are two different classifications for the Scandinavian languages, which are Insular Scandinavian and Continental Scandinavian.
According to  linguists  the Swedish language is a member of the latter, due to the influence of East Scandinavian primarily Danish languages.
Yes, in theory, but we understand each other here in Scandinavia - there is really only one language, `skandinaviska´, as we say.
Essentially, one Scandinavian language may be understood perfectly well by the user of another Scandinavian language.
In passing, Swedish-speaking finnish are under threat nowadays.
The whole Finland lives highly regressive mode, the old ghosts rising to the surface.