Number of e-books in my native language (Turkish) being scarce, and some books I wanted to read not being translated into Turkish, I had to start reading e-books in English last year.
I usually read fiction, mostly fantasy novels and thrillers.
Apart from vocabulary I don't face many problems. I have never built a rich vocabulary. Never learned any definitions by heart when our poor high school teachers kinda forced us to
BTW the main reason I use e-readers is because they provide built-in EN->EN dictionaries, allowing me to look up unfamiliar words with just a tap, however I forget the meaning just minutes after and look up the same word again and again each time I face it. Kinda like a fish I am
I should mention here that playing computer games greatly helps learning English. That is how I learned most of the stuff. I have never been to an English-speaking country, not even for a few days, but I bet it would have helped if I did.
I am sure there are people like that out there, so show your face! Tell us about what your native language is, about what helped you in learning English, the reason(s) why you prefer to read in a foreign language, what kind of books you read, about the ups and downs of reading in a foreign language, about the difficulties you face or maybe give some tips to others.