Dialects, Languages...dialectics

One of the tests people use to differentiate "language" from "dialect" is
mutual intelligibility. You can say that people speak the same language -- or a
dialect of the same language -- if they understand each other. If they don't
understand one another, they must be speaking different languages. That seems
like a good rule. So why, in a case like the Cologne and Bavarian dialects,
which aren't mutually intelligible, don't the Germans call them separate
languages? Or why are Swedish and Norwegian separate languages, when Swedes and
Norwegians have no trouble understanding one another? It's really pretty
confusing.

source: The 5minute Linguist