No Browser extensions available. You can either run it manually, clicking the bookmark everytime you join a plug.dj room, or have it automatically load if you have an Userscript extension installed (i.e. Tampermonkey or Greasemonkey). Demonstration

Select the text below, and drag it to your bookmarks

javascript:(function(){$.getScript("//rawgit.com/Burkes/plug-translator/master/dist/plug-translator.min.js")})();

Or click to install it as an Userscript