Removing the languages manually is too much work. I use XSlimmer (shareware) or Trimmit (free) to remove unnecessary bloat (languages, FAT binaries, compresses TIFFs, etc.). Trimmit appears to be a bit smaller, but doesn't keep a database of blacklisted applications which do no like being trimmed. Overall I prefer XSlimmer, but it was $12, instead of free. Both can make backups of the application before the trimming in case something goes wrong.

XSlimmer saved about 2gb on the standard MB Air install.

I also saved several gigs by deleting iMovie, iDVD, Garage Band, unused printer drivers. Make sure to also delete their theme files in your application support folder.

In addition, the Alex voice also takes up about 640 mb of space. HD/System/Library/Speech/Voices