I believe the most accurate translator engine today is Google translate. Even the translator in the iphone is garbage.
But I recently read an article, i cant remember where, saying that they made surveys for the google translate accuracy. It includes maybe aroud 80 participants. What amazed me that they found english-tagalog translation is around 95% based on their survey. English spanish is around 85%. But other english to another language pairs translation accuracy go very low down to 50%.