Jquery validation - regex greek text

Hello experts.
I'm using jquery validation plugin (http://www.position-absolute.com/)
The problem i have is to validate greek text.(allow greek text to pass the validation)
The plugin has  the regex for only letters:
"onlyLetter":{ "regex":/^[a-zA-Z\ \']+$/,
 "alertText":"* Only text allowed"},

I tried this one:
"onlyLetter":{"regex":/^[^\x00-\x80]+$/,
(from here:http://stackoverflow.com/questions/150033/regular-expression-to-match-non-english-characters)
This does not allow english(latin) letters.
Any help?