Simply put, if you put a high value on your foreign communication skills and / or have a need for them because you are working or living in a foreign country, then you can learn or is even necessary to learn their language.
But for people who live in their own nation, or who speak a language ( such as English ) wherein both the speaker and the listener are both comfortable using, learning extra languages is fun, but of little to no practical application.
When the fields of science and mathematics are getting more and more advanced, there is not much there to justify the necessity of learning more languages.
Music and photography are both really fun hobbies for some, as with being / learning to be a polylinguist. But there is no immediate necessity for the average guy to learn two or more languages.
The bottom line is, it isn't necessary but it could be fun or useful to you.