One of my challenges learning Norwegian has been dialects. There is a "standard" written form. The dialects, however, might pronounce things differently, completely change a few words, or change the way you use or conjugate verbs. (Not to mention that there are 2 varients of Norwegian, but that's another story.). Immigrants are taught the straighforward version - an "Oslo dialect".

The reason for this is mountains and isolation. You get a few villages that interact or a region that does so, and it varies wildly over the years before television and radio. People have simply kept the dialects in the modern age. Some are harder for native Norwegians than others, but supposedly they should all be understood.