Quote Originally Posted by Lt. Columbo
It may be helpful (what may? books or rosetta)
Both.
Quote Originally Posted by Lt. Columbo
Especially self-study books (what does this refer to).
To "not enough to learn the language very well".
Quote Originally Posted by Lt. Columbo
When I had read these books (except dictionaries) (what happened when you read these books? was it helpful or not)
When I had read these books I could read and understand pretty well, so it was helpful, but I couldn't understand a word watching a movie, so it was not enough to learn the language very well.
Quote Originally Posted by Lt. Columbo
just trying to clear the sentence up a bit
Is it clearer now?