<?
$string = "üáéøçí";
$chars = array(
"ü" => "u",
"á" => "a",
"é" => "e",
"ø" => "o",
"ç" => "c",
"í" => "i",);

foreach ($chars as $char => $char2) {
        $str = strpos($string, $char);
        if ($str) {
                $string = str_replace ($char, $char2 , $string);
        }
}
echo $string;
?>

prints: üaeoci