Okay so firstly, yup that’s a pretty cool application. Amazing in fact. Instant translations, on the screen, in situ, as in right there in the camera view, of signs etc. Awesome.
Secondly, The Economist seems to be using an online application called Apture. If you highlight some text on the page, you get a “Learn more” contextual link. If you click on that you get a floating div with relevant search results from Wikipedia, The Economist and more… I’d never seen that before but I like it. A good idea well implemented.