When I was growing up in London in the 1960s I used to hear my mother talking on the phone in Yiddish. I figured out that she was saying something she didn’t want me to understand, probably about a poor school report or a surprise birthday present. It never occurred to me that what I was hearing represented one terminal point of a great ‘language chain’ stretching back to Hebrew and Aramaic in ancient times. Even when I learned Yiddish formally so that I could use Jewish newspapers for research, I believed that it had been gestated in medieval Europe. But thanks to a remarkable coterie of experts, eccentrics and enthusiasts, Yiddish is undergoing a revolution.