"I have a book and (I) want to read it." is the second "I" really needed?
not always in English the second I is needed because if you read the sentence without it, it is not going to change the context of the sentence. so it doesn't really matter
the unnecessary second "I" is still not fixed. Reported on 11 July 2018.
Not definitely required, but the it is used in English to emphasize that you want to read this book specifically.