$string = preg_replace_callback('/\\\\u([0-9a-fA-F]{4})/', function ($match) { return mb_convert_encoding(pack('H*', $match[1]), 'UTF-8', 'UCS-2BE'); }, $string);
$string = preg_replace_callback('/\\\\u([0-9a-fA-F]{4})/', function ($match) { return mb_convert_encoding(pack('H*', $match[1]), 'UTF-8', 'UCS-2BE'); }, $string);