[ReCom]

Originally Posted by dimitrisvb

Now, if you only had some advice as to how I could arrange it so that only greek letters are accepted for usernames!

You would need to use regular expression (regex) for that:

1. Go to AdminCP > vBulletin Options > User Registration Options.

2. Look for setting "Username Regular Expression".

3. Now let say you want to limit the usernames to those containing a, b, c, d or e only. You would need to write in the setting:

^[abcde]$

4. So to allow greek characters only you need to replace 'abcde' with a string of all greek characters. Quite a long string I'd imagine

Perhaps there's a better way, probably using plugin. Will look into it further.

EDIT:
you can add plugin that hooks to register_addmember_process:

1. Check if $vbulletin->GPC['username'] is valid (greek characters only) using any PHP algorithm you want.
2. If it's invalid, append array $userdata->errors with your error message.