Harry Potter is an exciting story about young witches and wizards at school, and a story that every child knows, and many adults too. Therefore, reading the French translation is a great way to improve your skills at reading in French. Obviously the story is better in the original english, but the French translation is still incredibly well thought out. Words unique to the books are translated by new words that help to capture the feeling of the original, and there are also many examples of idiomatic expressions that you would otherwise never know until you were at a more advanced level. Reading in a foreign language helps you to become confident on your own in the language, and the French translation of Harry Potter is a great way to get started. One word of warning, many verbs are in the past historic, a tense that is only found in literature and not taught until A-level, however, this is more to do with the fact that it is rarely seen rather than because it's difficult, it is in fact pretty simple and so you should find you pick it up while reading.