Oh sweet lord you really did screw up.
Your going to have to boot into Single User mode and follow these commands to set your password to nothing so you hopefully can press enter and get in.
The Easy Password Reset Way. (no disk required)
1: Reboot the machine holding Command and S keys,you'll boot into single user mode.
2: Type in each command below followed by Enter or Return (you might have to wait a bit)
mount -uw /
(where "username" is the users name of the password yourtrying to change)
If you don't know the name of the users then enter
and you'll see three items: .localized, Shared, and a "username"
That should get you into your machine, but I don't know what's going to happen after that without a language.
Once you have copied off all your data to a another drive, then hold c and boot from the disk that comes with the comptur and reinstall OS X.
If that don't work then your going to have to reformat the drive in Disk Utility then reinstall OS X, all your programs and files from backup.
Changing passwords won't help because if I get to the password screen on my MBP, the point is that Monolingual screwed up my ability to type at all, I'm assuming because it erased the English language. I'm surprised I can type in the single user mode! I think my only hope is when Lion comes out to buy a copy here in Costa Rica somewhere & to HOPEFULLY be able to boot from that.