I decided to transliterate the URL from Cyrillic to Latin. In the file utils.inc.php I added:

function uriFilter ($s, $aParams = [])
{
    $sEmpty = isset($aParams['empty']) ? $aParams['empty'] : '-';
    $sDivider = isset($aParams['divider']) ? $aParams['divider'] : '-';
        // --- transliterate ---
    $aFrom = array(
    'а','б','в','г','д','е','ё','ж','з','и','й','к','л','м','н','о','п','р','с','т','у','ф','х','ц','ч','ш','щ','ъ','ы','ь','э','ю','я',
    'і','ї','є','ґ',
    'ў','ґ','ћ','đ','џ','č','ć','ž','š',
    'ә','ң','ғ','ү','ұ','қ','һ','ө','ұ'
     );
    $aTo = array(
    'a','b','v','g','d','e','e','zh','z','i','y','k','l','m','n','o','p','r','s','t','u','f','h','c','ch','sh','sch','','y','','e','yu','ya',
    'i','yi','ye','g',
    'u','g','c','dj','dz','c','c','z','s',
    'a','n','g','u','u','k','h','o','u'
     );
    $s = str_replace($aFrom, $aTo, mb_strtolower($s, 'UTF-8'));

Is everything I did correct — does anyone know? Will this solution cause any errors in operation? And is there any way to prevent my code changes from being removed during the next update?