preg_replace arabic title like مرحبا-اهلاً-بك-هنا

guys i have tried a lot of function but no one of them help me the way that supposed to be.

i have htaccess to replace URL to freindly URL like (test-test-test-test)

in english everything works fine but in arabic not work (مرحبا-مرحبا-مرحبا-مرحبا) not working probably

// English function work fine! replace long title with dashes 
// ex: hello-world-how-is-everything
    function seoUrl($string) {
        $string = strtolower($string);
        $string = str_replace('&',' ',$string);
        $string = preg_replace("/[^a-z0-9_s-]/", "", $string);
        $string = preg_replace("/[s-]+/", " ", $string);
        $string = preg_replace("/[s_]/", "-", $string);
        return $string;
    }

so i want it to be work in arabic language..
thanks