When translating phrases like these where the literal meaning does not exist in English, we either leave it as "itadakimasu" and make some notes on it at the end of the episode or at the top of the screen when it is said, or find the closest meaning to fit the context. In this case, "let's eat" will do fine. Most people who've watched a number of anime series should know the actual meaning already. Please try not to let these minor issues bother you; we try to bring you, the fans, the best out of any anime we sub. Also, thank you for your continued support by downloading our releases.