A new function instead of strtolower

[definitive]

Hello,
strtolower functions doesn't work correctly for Turkish language, because of İ,Ş,Ğ,Ü,Ö,Ç letters.
Is it possible to write a function for them for case conversion?
thanks

[definitive]

ok i have found

function strtolower_tr( $metin )
{
    return strtolower(strtr( $metin,'ĞÜŞIİÖÇ','ğüşıiöç'));
}