On the Mac, system files can actually take up quite a bit of space. If you purchase a new Mac, it will come preinstalled with language support for a lot of languages. Most people only need to use one language, so the language support simply is unnecessary.
I like MacCleanse. This program has some preset templates for cleaning up your system, and even the "Default" set is pretty thorough. It will delete all the languages that you do not need (in my case, everything but English), and it will also delete temporary Internet files, library reference files that are not needed, and so on. On the first scan of my system, it found nearly 3GBs of data that I did not need! One additional feature of MacCleanse is that you can schedule regular cleanings of the system. I like any program that can automate important tasks for you. It's just like backing up your computer, if you have to think about it you are likely not going to do it.