The song, which is first sung in episode 3 of the first season, is presented as in "Asgardian", but the language used is plain and simple Norwegian (though the accent is not the neatest).
Song written by Erlend O. Nødtvedt and Benedicte Maurseth.
Season 1, episode 3: "Lamentis"
Title: Jeg saler min ganger (I’m saddling my mount)