通过设置正确的HTTP header，解决下载文件时Unicode文件名乱码的问题。Set proper header to make Unicode filename works in major browsers.

attachment-headers.php

<?php
//
// Set proper header to make Unicode filename works in major browsers.
// see http://stackoverflow.com/questions/93551/how-to-encode-the-filename-parameter-of-content-disposition-header-in-http
//

$filename = '一个文件.txt';

$ua = $_SERVER["HTTP_USER_AGENT"];

if(preg_match('/MSIE (?:6.0|7.0|8.0)/', $ua)) {
  header('Content-Disposition: attachment; filename="'.rawurlencode($filename).'"');
} else {
  header('Content-Disposition: attachment; filename*=UTF-8\'\''.rawurlencode($filename));
}

header('X-Content-Type-Options: nosniff');

header('Cache-Control: max-age=0');