This also works if you pickup a series halfway through, having read the first half in your native language, and then finishing it in the new language. I've done this with Harry Potter. Before moving to Canada at 14, I read the first 4 in Romanian and the 5th and/or 6th in English. Since many of the terms were found in previous books, or since i knew them from the movies (example quidditch which the translators decided to translate. Still not sure how they got with the Romanian term from quidditch)

That's a great idea, because you already know the story, so you can sort of figure out the words you don't know due to your knowledge of the story.