Out on a sunny Berlin balcony, Tim Keeley and Daniel Krasa are firing words like bullets at each other. First German, then Hindi, Nepali, Polish, Croatian, Mandarin and Thai – they’ve barely spoken one language before the conversation seamlessly melds into another. Together, they pass through about 20 different languages or so in total. It can be difficult enough to learn one foreign tongue. Yet I’m here in Berlin for the Polyglot Gathering, a meeting of 350 or so people who speak multiple languages – some as diverse as Manx, Klingon and Saami, the language of reindeer herders in Scandinavia....