This work fine to me:
<?php
function normaliza ($string){
$a = 'ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞ
ßàáâãäåæçèéêëìíîïðñòóôõöøùúûýýþÿŔŕ';
$b = 'aaaaaaaceeeeiiiidnoooooouuuuy
bsaaaaaaaceeeeiiiidnoooooouuuyybyRr';
$string = utf8_decode($string);
$string = strtr($string, utf8_decode($a), $b);
$string = strtolower($string);
return utf8_encode($string);
}
?>