define("UPPER_WITHOUT_DIAC", "AAAAAACEEEEIIIINOOOOOOUUUUY" );
define("LOWER_WITH_DIAC", "àáâãäåçèéêëìíîïñòóôõöøùúûüý" );
 
function to_upper_without_diac($str) {
    $str = strtoupper(strtr($str, LOWER_WITH_DIAC, UPPER_WITHOUT_DIAC));
    return strtr($str, array("ß" => "SS" ));
}