custom collate like sort function PHP

my-collate-sort.php

function compare_by_alphabet($str1, $str2) {

    $alphabet = "AaÀàÁáÂâÅåÃãÄäÆæBbCcÇçDdÐðEeÈèÉéÊêËëFfGgHhIiÌìÍíÎîÏïJjKkLlMmNnÑñOoÒòÓóÔôÕõÖöØøPpQqRrSsߊšTtUuÙùÚúÛûÜüVvWwXxYyŸÿÝýZzŽžÞþ0123456789";
    $l1 = mb_strlen($str1);
    $l2 = mb_strlen($str2);
    $c = min($l1, $l2);

    for ($i = 0; $i < $c; $i++)
    {
        $s1 = mb_substr($str1, $i, 1);
        $s2 = mb_substr($str2, $i, 1);
        if ($s1===$s2) continue;
        $i1 = mb_strpos($alphabet, $s1);
        if ($i1===false) continue;
        $i2 = mb_strpos($alphabet, $s2);
        if ($i2===false) continue;


    if ($i2===$i1) continue;
        if ($i1 < $i2) return -1;
        else return 1;
    }
    if ($l1 < $l2) return -1;
    elseif ($l1 > $l2) return 1;
    return 0;
}

$names=["Schön","Åsberg","Zierer","Ås","Žižek","Schon","Asber"];
usort($names, 'compare_by_alphabet');
var_dump($names);