Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.
addOnloadHook(
  function() {
  var i = 0;
    while(i < watchlists.length) {
          mw.util.addPortletLink('p-cactions', 'http://en.wikipedia.org/w/index.php?title=' + watchlists[i] + '&action=edit', 'watch (' + (i + 1) + ')', 'ca-watch' + (i + 1))
      i++
    }
  }
)