We live in a diverse world. Some parts of it are dominantly monolingual and others are quite multilingual. Yet, even monolingual nations have polyglots among its citizenry. It is not uncommon to come across people who can comfortably speak three languages. In countries like India, it is quite normal to see people go about their everyday lives communicating in four-five languages. But how many languages is it really possible for a person to learn?
The answer is that there is no upper limit. Atleast, scientists haven’t found any as of yet. There is no reason a person shouldn’t be able to acquire thirty or forty languages.
However, if you are to interview polyglots, most are quite reluctant to admit knowing more than fifteen language. It has more to do with their humility and how they perceive fluency in a language. These people may be familiar with atleast a dozen or two more but they still believe they can be better at them. It really all boils down to how much time and patience you have for practice. If you have sufficient of both, there is no reason you cannot keep expanding your language skills.