Gold includes the original and add-on in a single haulable package. 13 new cities are added with Go East, spanning across Poland, Czech Republic and other 'East' places.
Currently the routes are limited to the UK, Belgium, Italy and the Netherlands. That's hardly enough for our empire of trucks - they're hungry to invade new (old) lands.
Euro Truck Simulator 2 Go East and its Gold bundle releases on PC September 20th for £10 and £30 respectively.