My vote is introvert. Biggest clue? How he handles his tennis, especially on court.
Introverts are inwardly focused. Federer never looks at his box, never talks to his box. He tries to figure it out himself. He didn't even have a coach for so many years.
Extroverts are outwardly focused, like Nadal and Djokovic, always talking to their box, always looking to their box for support.
The ability to give good answers in an interview is related to intelligence, not introversion or extroversion. Big misconceptions here in this thread.