Monolingual is a freeware application that deletes all the extra languages on your Mac, in an attempt to free up disk space. By removing all the files kept by unused languages, substantial space can be freed up. For instance, you would have to be a tremendous Star Trek geek to even think of using the Klingon language on the Mac, but a default install includes it.
Other options, such as keyboard layouts, can also safely be removed. The ability to remove Architectures is available. This is an option to select only if you are sure you want to remove them, backwards compatibility can be affected.
Users must proceed with caution. Make sure that you go through the long list of available language options and check only the ones you are sure you are not going to use. I left English and US English, and removed everything else. The only way to replace files is with the Mac OSX install disc. Again, be careful- the defualts must be checked carefully!
After running Monolingual, I was able to reclaim 2.4GB of space from the factory install on my MacBook. The program run took quite some time, make sure you will not run out of battery (or keep the box plugged in) during the process.