1. A method comprising: translating source language content in a source natural language to a target natural language using statistical machine translation (SMT) employing a conditional translation probability conditioned on the source language content; and optimizing values of parameters of the conditional translation probability by an iterative optimization process operating on a translation pool, the optimizing including adding candidate aligned translations to the translation pool by sampling available candidate aligned translations for a source language sentence in accordance with the conditional translation probability; wherein the SMT and the optimizing are implemented by a SMT system embodied by at least one digital processor.