"He speaks bad Swedish."
Translation:Han talar dålig svenska.
Oh, because its not an adverb here. "He speaks swedish badly" would be an adverb, but in "he speaks bad swedish" bad is describing "swedish", not "speaks", and "swedish" is an "en" word. (at least that's what I think). It's a weird one because the overall meaning of the sentence is to describe how he speaks-sortof!
In English at least, it would be more grammatically correct to say "He speaks Swedish badly". There really isn't such a thing as "bad Swedish" and "good Swedish. It is just Swedish, and a person either speaks it well or speaks it badly. I think this particular exercise should be changed.