"They do not read the book, they watch it."
Translation:Nem olvassák a könyvet, hanem nézik.
It would be closer to the Hungarian, yes.
Unlike Hulk014, I think that it's a perfectly good English sentence and that it expresses what the Hungarian does, just a bit more implicitly. (Well, I'd use a semicolon rather than a comma, but otherwise I think it's fine.)
"however" is wrong, I think, but "but instead" could work or just "instead" or "rather". (And "instead" could go at the beginning or the end of the second part.)
- They do not read the book, but instead they watch it.
- They do not read the book; instead, they watch it.
- They do not read the book; they watch it instead.
- They do not read the book; rather, they watch it.
No. No. No. No. No to all 4 of those examples. Translating "hanem" may make you feel like you're getting closer to the Hungarian, but it just makes your English sound unnatural. Echoing a negative with a parallel affirmative is all English needs or wants in establishing the contrast that Hungarian sets up with "hanem." Here are several more examples where Hungarian would need "hanem" but where English wants nothing to do with it:
-- The dress isn't red, it's blue.
-- I'm not eating chicken, I'm eating fish.
-- The children aren't talking, they're shouting.
-- We're not on vacation, we're at work.