To wish someone 'Happy Eating' in Italian, the most common phrase you will come across is buon appetito which actually literally translates to 'good appetite'.
The Origins of the saying 'Happy Eating'
Although the origin of the phrase is not verifiable, there are a number of myths about how it came to be part of common table-side etiquette. One suggestion is that at medieval banquets, the lord of the manor and his guests would feast upon a lavish spread whilst the serfs and peasants awaited a signal before feeding on the scraps; this signal came in the form of the lord exclaiming buon appetito! opulently.
Although the use of the phrase is considered a politeness on part of the host, modern etiquette experts suggest that the use of the phrase is improper because it awkwardly obliges guests to reply grazie, altrettanto or 'thanks, and to you'.
Alternatives like buon pranzo or buona cena ('good lunch' or 'good dinner') are occasionally used, perhaps because some Italians suggest that wishing someone a good 'appetite' shouldn't be necessary if the quality of food served is appetizing enough to ensure that the diner wouldn't need to have a particularly large appetite or to be very hungry in order to enjoy what is being served.
Despite this criticism, the phrase is still used at tables across Italy and will continue to be part of the Italian table-side lexicon.