Just learn them, dude. If you've learned one language (and understand it) picking up another is usually no trouble at all, especially nowadays when there are tons of tutorials, manuals, and support forums available for free.
Figuring out how to learn another language on your own is probably one of the most important skills you can master because the language is used in your school classes (no matter what it is) is very unlikely to be the "hot" language ten years from now.
Learning another language is also an excellent way to discover new ways of thinking about programming.
As to why those other languages are more popular, there are a number of reasons. Less boilerplate required to get something running, no compile step, dynamicity...(and of course there are also drawbacks -- type safety and so on).