$cur = array('Ö','ö','ç','ş','Ş','ı','ğ','ü','Ç','İ','Ü');
$cha = array('o','o','c','s','s','i','g','u','c','i','u');
$degisken = str_replace($cur,$cha,$degisken);
$degisken = str_replace(' ','-',$degisken);

<? 
function cevir($metin) { 
$metin = str_replace("Ç","C",$metin);
$metin = str_replace("Ğ","G",$metin);
$metin = str_replace("ı","i",$metin);
$metin = str_replace("İ","I",$metin);
$metin = str_replace("Ö","O",$metin);
$metin = str_replace("Ü","U",$metin);
$metin = str_replace("Ş","S",$metin);
$metin = str_replace("ç","c",$metin);
$metin = str_replace("ğ","g",$metin);
$metin = str_replace("ö","o",$metin);
$metin = str_replace("ü","u",$metin);
$metin = str_replace("ş","s",$metin);
$metin = str_replace(" ","-",$metin);
 return $metin; 
} 

echo cevir("ç Ç İ ı Ğ ğ Ö ö Ü ü Ş ş I i");

?>