php-unicode/lib/unicode.php

<?php

class UnicodeShim
{
    public static function bind()
    {
        static $init;

        if ($init++) return;

        function uchr($ord)
        {
            return json_decode('"'.'\u'.dechex($ord).'"');
        }

        function U($ord)
        {
            return uchr($ord);
        }

        function uprintf($arg)
        {
            $str = call_user_func_array('sprintf', func_get_args());
            $str = preg_replace_callback("/(\\\\u[0-9a-f]{1,4})/i", function ($chr) {
                 return json_decode('"'.$chr[1].'"');
            }, $str);
            echo $str;
        }

        function usprintf($arg)
        {
            $str = call_user_func_array('sprintf', func_get_args());
            $str = preg_replace_callback("/(\\\\u[0-9a-f]{1,4})/i", function ($chr) {
                 return json_decode('"'.$chr[1].'"');
            }, $str);
            return $str;
        }
    }
}

UnicodeShim::bind();