I'm a native speaker of Swedish. English is my second language, and I speak it quite fluently, and Duolingo tells me I know 56% French.
I also studied German in school, and if you hand me a German text, I will still be able to make at least some sense of it, even though my knowledge has atrophied a bit from lack of use.
Also, being Swedish, I can understand some of the dialects of Norwegian that are most similar to Swedish. It basically sounds like Swedish with a funny accent and a few changed words. The more dissimilar accents are pretty incomprehensible to me, though. Same with Danish.