My wife is a Québecoise, and when we sit down at the table we always say “Bon appétit.” When I visit Germany it’s “Guten Appetit,” and in Italy, “Buon appetito.” Omniglot.com lists similar expressions in scores of languages, including Kazakh, Korean and Klingon, but observes that “There is no exact English equivalent.”  The most I’ve heard said before a meal in English is grace. My parents were observant Roman Catholics but we never said  grace, and the only time I remember grace was the year I spent in a Jesuit boarding school. According to the OED, the custom of saying grace (usually in Latin) was adapted by the early Christians from the Greeks, Romans, and Jews, but it seems to have survived strongest in America. I prefer “Bon appétit,” or as my Polish friends say, “Smacznego.”