Beats the hell outta me...search your disk for 'en-US.jar' and it'll be the one that's NOT in your 'chrome' folder.
Update: apparently you found it - for some reason, the posts where you found it didn't show up the last time I saw this thread. Oh, well.
When Moz. 1.1 comes out, there's a good chance that the en-US.jar file will not be the same as the one you've got, but you may be able to keep the old one. It's worth a try, anyway. I'll be editing the new one if it doesn't work.