urldecode() function is not supporting UNICODE characters coding, like %u0627 for the Arabic letter ALEF (ا in HTML). So when you are passing the Unicode chars through GET/POST or urldecode(), you will get only encoded string:

http://server.com/test.php?test=%u062D%u0645%u0627%u062F%u0629

in test.php:
print('test = '.$test);

you will get:
test = %u062D%u0645%u0627%u062F%u0629

What you have to do is to "manually" convert it to html entitles:
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function unicode_decode($txt) {
  return ereg_replace('%u0([[:alnum:]]{3})', '&#x\1;',$txt);
}
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