For me, it went the other way around: I became an avid reader because I started learning German. It has a whole wealth of literature you can choose from, and I don't even regret the fact that I've spent hours on end every day with my dictionary trying to decipher Kafka ( I was A2 at the time, very tough).

But I'm sure I'd have felt the same if I picked any other language with a reasonable number of speakers. Literature was for centuries used as a form of cultural expression, through which one could understamd the POV of the respective people. How does a certain people group think, their traditions etc are just as important to understand as the language per se, as you can finally understand where a native is coming from when he is telling you that whatever sentence doesn't sound or "feel" natural.

If you're interested in the number of books you can access to, choosing one of the major languages is the way to go. Otherwise it's up to you to decide which language has produced the best literature.