中英文字符串翻转函数

<?php
//页面编码设为utf8
header(Content-type: text/html; charset=utf-8);
$luokuan = "ABCDEFG-测试的啊-!!!一二三四五 。 。";
$n = mb_strlen("$luokuan","UTF-8");
//echo $n;
$newluokuan = "";
for ($i=$n;$i>=0;$i--)
{

$newluokuan.= mb_substr($luokuan,$i,1,UTF-8);

}
echo $newluokuan;
?>