for cyrillic and UTF 8 use mb_convert_case
exampel
<?php
$string = "Австралия";
$string = mb_convert_case($string, MB_CASE_LOWER, "UTF-8");
echo $string;
//output is: австралия
?>
for cyrillic and UTF 8 use mb_convert_case
exampel
<?php
$string = "Австралия";
$string = mb_convert_case($string, MB_CASE_LOWER, "UTF-8");
echo $string;
//output is: австралия
?>