Sanitisation does not allow non latin characters

I tried to import a few hundred users with Greek usernames and all names came up as sequences of 2. I think this happened because the first one was replaced with an empty string as the Greek characters were not allowed. And then a 2 kept being added to avoid duplication of existing names.

As soon as I removed this line (1173):

$username = preg_replace('/[^a-zA-Z0-9@ ]/', ' ', $username);

it worked without a problem.

So maybe the sanitisation needs to be less strict.