I've read the Harry Potter books a bunch of times and decided to try to read it in German! Something fun about those books is each book is written at the same level as the age of Harry. So the first book the language and vocabulary is a bit more simple since he's 11 years old, and as the books go on and he gets older, the language/vocab gets more complex. For learning a new language, I found this incredibly helpful! Partially because I have a general idea of what's happening due to knowing the English books so well, partly because it's written at a level I can manage.