Do this little experiment:
- Navigate to your Applications folder in the Finder.
- Click on the iTunes application icon.
- Press CMD-I, select Get Info from the File menu, or right-click and select Get Info.
- Press the triangle geegaw next to Languages.
- Click on any language other than English.
- Press the Remove button.
- Press RETURN at the alert prompt.
- Notice the iTunes application file size go down measurably.
- Repeat with any other undesired language packs.
- Close jaw at file size savings.
On the iTunes application paring, I went from 18MB to 6.8MB just by getting rid of languages that I'll never use. My hypothesis for this experiment is that you're going to go through every application (or nearly all of them) looking for other languages to trim. I did and I shaved off over 200MB of space. Now, there's nothing stopping a system update or application upgrade from completely undoing your effort but you can at least enjoy the savings for now. I would also consider trimming iPhoto as that is one bloated by language resources.
Credit goes to this Slashdot comment. Applications that do this sort of thing routinely are Monolingual and DeLocalizer. I'll probably use DeLocalizer in the future, but I think it was an important experiment to do by hand the first time.