I'm a second language teacher, and explain to my (adult) students how to choose a book that is at the right (stretch) reading level for them, so they can make informed choices about their fun reading. It’s not at all uncommon for them to have to read academic or subject texts way before their language ability is there, though.

I had to as well and it absolutely takes the fun out of reading and absolutely improves your reading ability (as long as you get enough feedback to make sure you are in fact comprehending the material). Some students want that and some students don’t.