mdc_ja_link_to_en

// ==UserScript==
// @name           MDC link to en
// @namespace      http://rails2u.ocm/
// @include        https://developer.mozilla.org/ja/*
// ==/UserScript==

(function () {

//var links = $X('//a[@rel="internal"]');
var links = $X('//a');
var re = new RegExp('/ja/', 'i');
var locationEN = location.href.split('#')[0].replace(re, '/en/');
links.forEach(function(link) {
  var url = link.href;
  var hashLink = (url.indexOf('#') == 0);
  if (re.test(url) || hashLink) {
    var a = document.createElement('a');
    var en = document.createTextNode('[en]');
    a.style.marginLeft = '5px';
    if (hashLink) {
      a.href = locationEN + url;
    } else {
      a.href = url.replace(re, '/en/');
    }
    a.appendChild(en);
    if (link.nextSibling) {
        link.parentNode.insertBefore(a, link.nextSibling);
    } else {
        link.parentNode.appendChild(a);
    }
  }
});

function $X (exp, context, resolver) {
  context || (context = document);
  var Doc = context.ownerDocument || context;
  var result = Doc.evaluate(exp, context, resolver, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
  for (var i = 0, len = result.snapshotLength, res = []; i < len; i++) {
    res.push(result.snapshotItem(i));
  }
  return res;
}

})();