Can duolingo make you fluent?

If you work hard, every day and also read books, watch tv shows or movies and talk in the language you are learning, then the answer is yes. Duolingo helps you but doesn't do everything for you (and it can be more difficult to be fluent in languages like Arabic or Japanese with Duolingo).

Not really, no. Not on its own it can't. It's a great supplemental tool though, and great to start with as a beginner. Eventually, especially at intermediate levels, you'll need more practice speaking and listening organically.