PHP通过header下载文件中文名称乱码的解决办法？

如题。

                header("Content-Type: application/pdf; charset=utf-8");       
                $ua = $_SERVER["HTTP_USER_AGENT"];
                $filename ="你好.pdf";
                $encoded_filename = urlencode($filename); 
                $encoded_filename = str_replace("+", "%20", $encoded_filename); 
                if (preg_match("/MSIE/", $_SERVER['HTTP_USER_AGENT']) ) { 
                    header('Content-Disposition:  attachment; filename="' . $encoded_filename . '"'); 
                } elseif (preg_match("/Firefox/", $_SERVER['HTTP_USER_AGENT'])) { 
                    header('Content-Disposition: attachment; filename*="' .  $filename . '"');
                } else { 
                    header('Content-Disposition: attachment; filename="' .  $filename . '"'); 
                }