[UPD]:
I've just double-checked. It behaves this way under Nginx 1.17 only. Apache works fine!
The code:
$url = '/Регистрация/?lala=123';
$res = parse_url($url);
echo '<pre>';
print_r($res);
echo '</pre>';
Under Apache everything works fine. Under Nginx 1.17 it looks like below.
Any ideas?