[Sam Bauers]

You can potentially use “special” characters in usernames via a plugin, but with the ability to have separate “display” names it is not enabled in the core.

Putting this in a plugin might work on it’s own actually…

function my_sanitize_user( $username, $username_raw, $strict ) {

if ( $strict ) {

return sanitize_user( $username_raw, false );

} else {

return $username;

}

}

add_filter('sanitize_user', 'my_sanitize_user', 10, 3);