My wife is Norwegian, so I have some interest here ...
I would definitely conclude that it is related to Sven. Regional spellings and pronunciations often throw us off, but frequently it is just a substitution of several letters whose histories are entwined. The first name of the man you cited, Juernjakob, reflects a definite regionalism. I’d suspect that the name is actually from a combination name of: http://www.behindthename.com/php/view.php?name=jorunn
German is related to the Scandinavian languages though more closely related to English and Dutch. So if I were you, I’d check Sven in the First Name database at:http://www.behindthename.com/php/view.php?name=svein