Функция PHP mb_strtolower

string mb_strtolower ( string str [, string encoding] )

mb_strtolower returns str with all alphabetic characters converted to lowercase.

encoding specifies the encoding of str; if omitted, the internal character encoding value will be used.

By contrast to strtolower, 'alphabetic' is determined by the Unicode character properties. Thus the behaviour of this function is not affected by locale settings and it can convert any characters that have 'alphabetic' property, such as A-umlaut (?).

Пример использования mb_strtolower

   $str = "Mary Had A Little Lamb and She LOVED It So";
   $str = mb_strtolower($str);
   echo $str; // Prints mary had a little lamb and she loved it so

See also strtolower, mb_strtoupper and mb_convert_case.