Why doesn't preg_match work?

Question

PHP

If I write PHP code,

if (!preg_match('/\/ettevote\/filter\/abc\/([A-Za-z0-9-&ŠšŽžÕõÄäÖöÜü])/', $_SERVER['REQUEST_URI'], $code)) {
    die('Not found!');
}

and open the link /et/ettevote/filter/abc/ü , it gives NOT FOUND.

It is the letter ü that does not work, but az works with any letter of ordinary Latin.
How to fix?