A lot of the language that they use in harry potter is a made up language. So its it's a little bit difficult to read some of the dialogues because the spelling is strange, ok? A lot of slang and jokes that people who aren't from england might not understand. If you're just reading a novel just to study english, you're not going to get very much out of it. You have to actually want to read it. And i would recommend that you buy a book in english and read one that you would be interested in reading in your own language as well.