Change Username Charset

[nikosuk]

Hello
i am using tsse 5.6 nightcrawler release.
I would like to be able to use Greek characters in the username field,
so that some of my users couls change their username to the corresponding greek one.
I have tried changing the DB field "username" to several encodings but it doesnt seem to work
I cannot change the username from edituser.php and if i change it on the DB to greek i get ???????? (questionmarks)

Anybody has an idea?
Thanks for your time

Bump: Has anyone any solution for this?

thank you in advance

Bump: Anyone might have a clue on this ?
any help will be appreciated