1. A computer-implemented method, the method comprising: receiving a set of acceptable expressions, each acceptable expression being a string that identifies a value of a variable entity in a first natural language, each acceptable expression being associated with a canonical representation of the value identified by that expression; performing machine translation on each acceptable expression to obtain a translated expression of the acceptable expression in a second natural language; associating the canonical representation associated with each acceptable expression with the corresponding translated expression in the second natural language; and providing a set of training data for a machine translator from expressions in the second natural language to the associated canonical representations, the set of training data comprising the translated expressions and the canonical representations that are associated with the translated expressions.