Description:
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Directory/Filesystem functions do not work with multibyte-strings.
When eg trying to open or move a file or directory with a chinese filename, the file or directory being accessed or created has a completely messed up name.
Could not find a work-around.

Reproduce code:
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// Multibyte support is enabled (UTF-8)

// change this correspondingly for your FS
$origFile = "c:/myfile.txt";

$chineseName = $_POST["filename"];

echo "name: " . $chineseName;
echo "len: " . mb_strlen($chineseName);
echo "sb-len: " . strlen($chineseName);

$dir = dirname($origFile);
rename($origFile, $dir . "/$chineseName") or die("Could not rename file: $origFile");

Expected result:
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name: 中文字.txt
len: 7
sb-len: 13


Actual result:
--------------
Actual filename is:
中文字.txt