Замена одинаковых английских и русских букв при поиске

<?PHP
function translit($str)
{
    $tr = array(
            "А"=>"A","O"=>"B","В"=>"V","Г"=>"G",
        "Д"=>"D","Е"=>"E","Ж"=>"J","З"=>"Z","И"=>"I",
        "Й"=>"Y","К"=>"K","Л"=>"L","М"=>"M","Н"=>"N",
        "О"=>"O","П"=>"P","Р"=>"R","С"=>"S","Т"=>"T",
        "У"=>"U","Ф"=>"F","Х"=>"H","Ц"=>"TS","Ч"=>"CH",
        "Ш"=>"SH","Щ"=>"SCH","Ъ"=>"","Ы"=>"YI","Ь"=>"",
        "Э"=>"E","Ю"=>"YU","Я"=>"YA","а"=>"a","б"=>"b",
        "в"=>"v","г"=>"g","д"=>"d","е"=>"e","ж"=>"j",
        "з"=>"z","и"=>"i","й"=>"y","к"=>"k","л"=>"l",
        "м"=>"m","н"=>"n","о"=>"o","п"=>"p","р"=>"r",
        "с"=>"s","т"=>"t","у"=>"u","ф"=>"f","х"=>"h",
        "ц"=>"ts","ч"=>"ch","ш"=>"sh","щ"=>"sch","ъ"=>"y",
        "ы"=>"yi","ь"=>"'","э"=>"e","ю"=>"yu","я"=>"ya"
    );
    return strtr($str,$tr);
}
?>
 
<form action="search.php" method="post">
<tt>
Поиск<input type="text" name="search" value="что искать?" onclick="search.value=''<?translit()?>;"/>
<br /><input type="submit" name="submit" value="искать"/>
</tt>
</form>

<input type="text" name="search" value="что искать?" onclick="search.value=''<?translit()?>;"/>