I've heard of plenty of people who say that are fluent in 5-6 languages but I seriously doubt that their level is actually at a point where the communicate easily and elegantly in all those languages. I've never actually met such a person to test my hypothesis. After all, I don't see the point of knowing so many languages. Obviously, English is a must, whoever you are on this Earth, it will improve your life, and give you better economical opportunities, thanks to the Internet. Then you may be passionate about a certain topic that's more developed in a certain country, like 19th century science papers are generally written in German, or German philosophy might be a reason to learn it. Or maybe you want to move to another country. But in that case, more than 4 languages are not providing a big benefit, not even an economical one. It's a situation of diminishing returns. And we have to consider the actual involvement required to maintain a working knowledge of more than 5 languages. I've personally seen myself slightly forgetting elements of my native language when not using it for extended periods of time. Sure those are particular domain-specific knowledge, but it does happen.