mysql - Output failure (No Output!) in PHP if umlaut/mutation in String -

if read text database, contains ü, ö, ä, , on -> function gives no output.

its not easy check errors because webhook called script.

example (like function):

 function foo() {      global $db_link;     $output = "names: ";      $res = mysqli_query($db_link, "sql");      while ($data = mysqli_fetch_assoc($res)) {     $output .= "desc1: ".$data['name1']."/";     }      return $output;     } 

here part of original function:

    $sql = "select * `member_cars` `car_memberid` = ".$profile_data['member_id'];     $res = mysqli_query($db_link_website, $sql);     $anzahl_erg = mysqli_num_rows($res);  if ($anzahl_erg>0) {         $return_var .= "❚ ".$anzahl_erg." fahrzeug(e):     ";        while ($data = mysqli_fetch_assoc($res)) {           if ($i==2) { echo $return_var .= "         ".$i." fahrzeug:         "; }           $return_var .= "         ".$data['car_displayname']."         • hersteller: ".$data['car_hersteller']."         • modell:     ".$data['car_modell']."         • hubraum:    ".$data['car_hubraum']."         • baujahr:    ".$data['car_baujahr']."         • leistung:   ".$data['car_ps']."         • treibstoff: ".$data['car_treibstoff']."         ";                 $i ++;                 }      }