This can go either way depending on the situation.
Generally, saying that someone thinks a lot of himself, or has a high opinion of himself means that he is conceited. However, if you say that someone is confident in his abilities, or he is self-assured this means almost the same thing without the negative connotations.
The reason that this can be confusing is because the difference between admirable self-assurance and obnoxious self-love sometimes exists only in the opinion of the person observing the behavior. I think this is the same in every language.