Description:
------------
Simply put, basename() does ot work with Japanese filepaths. If the
filename is Japanese only the extension part of the filename is
returned. So a filename "/folder/ファイル名.txt" resolves to just
".txt". I discovered the problem when performing a basename() on the
$_FILES array's 'name' element for uploaded Japanese files, however
after testing the bug occurs no matter how you supply the filename.

My PHP environment is running with UTF-8 internal encoding.

The code snippet below illustrates this perfectly.

Reproduce code:
---------------
<?php
// show normal behavior with roman filename
$filename='/myfolder/roman_filename.txt';
echo "The full filename of the romanized file is $filename.\n"; //
/myfolder/roman_filename.txt
$basename=basename($filename);
echo "The basename of the romanized file is $basename.\n"; //
/roman_filename.txt
// show behavior with Japanese filename
$filename='/myfolder/日本語のファイル名.txt';
echo "The full filename of the Japanese file is $filename.\n"; //
/myfolder/日本語のファイル名.txt
$basename=basename($filename);
echo "The basename of the Japanese file is $basename."; // .txt
?>

Expected result:
----------------
The full filename of the romanized file is
/myfolder/roman_filename.txt.
The basename of the romanized file is roman_filename.txt.
The full filename of the Japanese file is
/myfolder/日本語のファイル名.txt.
The basename of the Japanese file is 日本語のファイル名.txt.

Actual result:
--------------
The full filename of the romanized file is
/myfolder/roman_filename.txt.
The basename of the romanized file is roman_filename.txt.
The full filename of the Japanese file is
/myfolder/日本語のファイル名.txt.
The basename of the Japanese file is .txt.

Won't fix in PHP 5. This will be implemented for PHP 6.