Philosophy as an undergrad or postgrad is actually a very tough degree.I reckon plenty of idiots would tick both of those boxes. Speaking several languages is what happens when you grow up in a place where many languages are spoken. Most Europeans speak English plus their mother tongue. It's about exposure not intelligence.
A degree in philosophy just requires money and free time. In fact, if you live in a place where governments subsidise tertiary education (or guarantee loans) you don't even need money. Just free time.
That said, I don't think anyone could be capable of the level of success Djokovic has achieved if they were stupid, regardless of their work ethic or natural talent. He's obviously smart enough.