$degis = array ('ı','Å?','ü','ç','ö','Ä?','Å�','Ã�','İ','Ä�','Åz','Ã�','Ã�','ı','Å?','ç','ö','Ä?','Å�','Ã�','İ','Ä�','Åz','Ã�','Ã�','ü','Ä�');
$ara = array ('ı','ş','ü','ç','ö','ğ','ş','Ç','i','ğ','Ş','Ö','Ü','ı', 'ş', 'ç', 'ö', 'ğ', 'ş', 'Ç', 'i', 'ğ', 'Ş', 'Ö', 'Ü', 'ü', 'ğ');
$yeni = str_replace($degis, $ara, $yazi);mantık budur