While I don't know Greek, I'd be happy to look into this for you. As far as I know all you'd have to do is find someone willing to translate the script, or find a translated script. Then you could change the character set to match the script, or something along those lines.
I imagine changing the character set is something that's been done before around here, especially considering the Team Avalanche mod does an entire overhaul on the game's interface.
Cheers,
Corigne