Download YouTube Subtitle — Run this bookmarklet on a YouTube video page to download its subtitle.

bookmarklet.js

/* Created with YouScript Bookmarklet Editor
 * http://netj.github.com/youscript/
 */

var m = location.href.match(/youtube.com\/watch\?(.+[&])?v=([^&]+)/);
if (m != null) {
  var videoId = m[2];
  function askLanguageAndDownload() {
    var lang = "en";
    // figure out the first available language for subtitle
    var langSelector = document.getElementById("watch-transcript-track-selector");
    if (langSelector != null)
      lang = langSelector.value.substring(0,2);
    lang = prompt("Download subtitle for which language?", lang);
    if (lang)
      open("http://video.google.com/timedtext?lang="+lang+"&v="+videoId);
  }
  if (document.getElementById("watch-transcript-track-selector") != null)
	askLanguageAndDownload();
  else { // we need to click the Transcript button to get the language selector
    var btn = null;
    {
      var btns = document.getElementsByClassName("action-panel-trigger");
      for (var i=0; i<btns.length; i++)
        if (btns[i].title == "Transcript") {
          btn = btns[i];
          btns[i].click();
        }
    }
    if (btn != null)
      setTimeout(askLanguageAndDownload, 2000);
    else
      askLanguageAndDownload();
  }
} else {
  alert("Cannot recognize which YouTube video you are watching.");
}