Danish, Swedish and Norwegian is very similar (also a little bit of the german language. Because long ago Denmark, Sweden and Norway used to be a combined country, ruled by the Swedish king. Later on Denmark became independent country. And Norway was a combined country with Sweden. Norway tried to do everything they could to become independent. They did strikes, the people grew with anger. But the king of Sweden said no. Then one day, the Norwegian threatened the Swedish king, after all of those years, to become separate countries "If you don't make us an independent country, without you as our king and your politics, than we demand a war." Of course the king had enough of this and their threats, and that it has been over this for many years. Also a note that Sweden hasn't been in a war in hundreds (or thousands years, I'm not sure?) So the king said "Yes." on that day. Norway became an independent country on the 17th of May 1814. Norway and Denmark has been friends longer than they have been to Sweden. So that is WHY the Norwegian and the Danish spelling is so similar, but they pronounce almost the same way as Swedish.
That's why 'Norden' (Scandinavia) can understand each other very well if you spoke with each other by your own language (Norwegian, Danish and Swedish). The only difference's is that it's some of the spelling, maybe some of the grammar and that it's almost like talking to each other but a different accents. I know this because I'm from Sweden, but me and my mum are Norwegian. (I am also half English by the way.) And my mum told me a simple way on how Norway became independent and why all these three languages sound so similar.
You're very welcome!