Please try this solution. You have to add this code to your active theme’s functions.php file.
function wpdm_sanitize_chinese_user( $username, $raw_username, $strict ) {
if ( $username != $raw_username ) {
$username = $raw_username;
}
$username = strip_tags( $username );
// Kill Chinese characters
$username = preg_replace( '|[^a-z0-9 _.\-@一-龥]|ui', '', $username );
// Consolidate contiguous whitespace
$username = preg_replace( '|\s+|', ' ', $username );
return apply_filters( 'sanitize_chinese_user', $username, $raw_username, $strict );
}
add_filter( 'sanitize_user', 'wpdm_sanitize_chinese_user', 1, 3 );
