I lived in Norway for a year some years ago and spent 4 months getting fluent in the language most commonly spoken in Oslo. After mastering that, the dialects were just a matter of listening harder. It was more difficult to stay consistent with one dialect when speaking, however.
Each region had its own dialect, but it didn’t take a whole lot to figure the common roots of the words. The literary language was just a compromise between the dialects. You say potehto, I say potahto. Plus, the muhammedans moving to Norway should understand the “root word” concept of a language. It’s central to Arabic.