Not an easy language to learn, altho, not the hardest either, well, at least the rudimentary stuff. There's a lot of implicit things in our language, and double, even triple meanings of words depending on the sentence syntax and situation they are spoken in. Anyways, spanish or russian may be your better choice, since more people speak it. We are only 5,8 millions people in Denmark, altho learning danish will open up for Norwegian and Swedish as well, so that's another 12-13 millions or so
As for english, I am better at reading and hearing it, than writing it, but I am not bad at writing it either, just not perfect at all My german is nothing to write about (I am from an older generation, where we learned it later than they do now) but I understand the spoken german, and can sorta make head and tail of the written (being neighboors with Germany helps in that regard)
Anyways, if you want to learn danish or russian, go for it. There are free online courses to take, and cheap ones as well