Berlin’s state government claims the buy-back cost could be up to €36 billion for apartments it sold 20 years ago for €2 billion. Such money, it says, would be better invested in building new social housing. Photograph: Sean Gallup/Getty Images It was 2006, the Celtic Tiger was still roaring and the Irish visitor liked the Berlin apartment he was viewing so much that he bought two. Corkman Tim O’Leary (not his real name) had heard on the grapevine about a property sale of the century in Berlin. To plug a multibillion euro, self-inflicted hole in its budget, the city was...