translator.user.js

// ==UserScript==
// @name           translator
// @namespace      http://d.hatena.ne.jp/youpy/
// @include        *
// @require        http://github.com/cho45/jsdeferred/raw/master/jsdeferred.userscript.js
// ==/UserScript==

var div = document.createElement('div');
div.className = 'gm_translator';
window.addEventListener("mouseup", translate, false);

function translate(e) {
  with(D()) {
    var selection = window.getSelection().toString();
    if(selection && selection.match(/./) && selection.length < 400) {
      var url = 'http://translator.jgate.de/convert?q='
        + encodeURIComponent(selection)
        + '&to=ja&format=json';
      xhttp.get(url).next(function(res) {
        var json = eval('(' + res.responseText + ')');
        addTip(json.result,
               window.scrollX + e.clientX,
               window.scrollY + e.clientY);
      });
    }
  }
}

function addTip(str, x, y) {
  with(div.style) {
    left = x + 'px';
    top = y + 'px';
  }
  div.innerHTML = str;
  document.body.appendChild(div);
  window.addEventListener("mousedown", removeTip, false);
}

function removeTip() {
  document.body.removeChild(div);
  window.removeEventListener("mousedown", removeTip);
}

GM_addStyle(<><![CDATA[
  div.gm_translator {
    font-size: 12px;
    color: #fff;
    position: absolute;
    background: #000;
    padding: 0.5em;
    z-index: 999;
    max-width: 300px;
    opacity: 0.8;
    -moz-border-radius: 3px;
  }
]]></>);