If you're that pressed for space, take a look inside the /usr/share/locale directory. That directory contains modules for each locale that each program supports. If you only care about a single locale, you can delete the directories for the other locales. For example, my locale directory has 13 MB of data total, of which only 0.5 MB are for the en_GB locale. You can easily save several MB of space.

Be careful, though, because some programs only include language files for one or a few locales. Deleting all the language files for a certain program will lead to a very incomprehensible application.

By the way, I've never actually tried this on my N800, since I have plenty of space, so I can't be held responsible if you bork your system. Why don't you just do the ext2 extending-root-onto-a-memory-card trick?