It doesn't work on any system below PHP 6. You can always use the intl extension from PECL while waiting for proper unicode support: http://pecl.php.net/intl 

Using the collator (http://php.net/collator) you can achieve sorting with any locales.

On Linux strcoll works fine, I get only on Mac OS X (BSD) a false 
order. I also test it with a ISO 8859-1 string and locale 
de_DE.ISO8859-1. The same result, on Linux correct, on Mac OS X wrong.

So I think it's not a Unicode issue!

Here is another test code:

$string_utf = "abcdefghijklmnopqrstuvwxyz????";
$string_iso = utf8_decode($string_utf);

$array_utf = array(); $array_iso = array();

for ($i=0; $i<mb_strlen($string_utf, 'UTF-8'); $i++) {
    $array_utf[]=mb_substr($string_utf, $i, 1, 'UTF-8');
    $array_iso[]=substr($string_iso, $i, 1);
}

print("\nLocale: " . setlocale(LC_COLLATE, 'de_DE.UTF-8'));
usort($array_utf, 'strcoll');
print("\n" . implode('', $array_utf) . "\n");

print("\nLocale: " . setlocale(LC_COLLATE, 'de_DE.ISO8859-1'));
usort($array_iso, 'strcoll');
print("\n" . utf8_encode(implode('', $array_iso)) . "\n");


The result on Mac OS X:

Locale: de_DE.UTF-8
abcdefghijklmnopqrstuvwxyz????

Locale: de_DE.ISO8859-1
abcdefghijklmnopqrstuvwxyz????

And the Linux result:

Locale: de_DE.UTF-8
a?bcdefghijklmno?pqrs?tu?vwxyz

Locale: de_DE.ISO8859-1
a?bcdefghijklmno?pqrs?tu?vwxyz

I get the wrong order on Linux. Did you mix the results there? Anyways, this really is a problem in unicode support. To get _really_ working stuff, use the intl extension or wait for PHP 6. Wont fix.

What is your result on Linux? Do you saved the test file with UTF-8 
coding?

Because strcoll is basically a C function, I can't see why it is a PHP 
Unicode issue and why you close the bug as Wont fix.

The code for this function is just:

    RETURN_LONG(strcoll((const char *) Z_STRVAL_PP(s1),
                        (const char *) Z_STRVAL_PP(s2)));

We use the underlying system strcoll function.  There is nothing for us to fix here.  If your system's strcoll function is broken, you are out of luck.  OSX has a long history of buggy C99 functions and it wouldn't surprise me if the strcoll function doesn't handle UTF8 locales correctly.  But that still isn't something we can fix short of doing an OS-specific hack here which we try to avoid.