In the most cultures, some people say something before there meal. In French they say "bon appétit", In Belgium and The Netherlands "smakelijk" and in Polish "smaczny". But how can I say the same thing in English?
In US usage, there is no direct equivalent. You will find some people who use "bon appétit" occasionally. Also, someone might say "Enjoy your meal!". But I don't think either salutation is typical.
On the other hand, it would be fairly typical to ask, prior to eating "Are you hungry?", or, less commonly, "Got an appetite?". It would also be typical to ask, shortly after the start of a meal "How is the food?", or any number of variations on that theme.
Edit: it later occurred to me, as others had posted notes about both pre-meal prayers and the social and cultural intent of the phrasing in question, that US English, did, at one time, have a similar practice. Prior to the 1960's or 70's, a pre-meal prayer ("saying grace") was a prevalent practice. With the aging of the "baby-boom" generation, that practice fell out of favor. "Grace" was typically something short, and semi-formulaic. Thus, it was not something that would be directly parallel to “bon appétit” or “smakelijk”. However, if one considers the cultural intent more than the literal usage, one can find parallels. 1) It was a practice that "started" the meal. 2) It typically connoted a message of thanks, to the host, to the guests, to the sources of the food that made the meal, etc. 3) It often referred, in cultural context, to a hope that the consumers enjoy the meal. Obviously, “bon appétit” or “smakelijk” are linguistically and culturally much simpler than "saying grace", but under that simplicity is a cultural message that is inferred by their use.
Some Americans will pray over their food before they eat, but there isn't a customary phrase. When translating such phrases from other cultures (adding the example of Japan's いただきます, literally "I humbly receive"), the translators will often use something like, "Thank you for the food!"
The other phrases suggested, such as "Dig in!" "Are you hungry?" and "Bon appétit!" are usually spoken by the person providing the food, not by the one about to partake.
In some situations “Eat Hearty” may work.
It's much less formal than bon appétit, but if you are looking for a formal phrase you can just use bon appétit in English.
Perhaps trying to introduce a foreign custom into English conversation will simply be awkward.
Dining out in Spain, everyone who knows you stops by to say "Buen provecho" or even worse "Enjoy", since I'm an American, but in the US, interrupting someone's meal to say such a thing would simply be weird, as would the common Spanish practice of guests at a meal repeating "Buen provecho" around the table.
In American culture, only the person serving the food would typically say something before the meal, whether that something be "Let's eat" or "Bon appétit", or the rather savage "Dig in." My point is that, as a guest in someone's home, you definitely don't want to say "Enjoy (your meal)", because this is not for a guest to say. It may even be rude for a guest to do so.
On the other hand, I have known "Bon appétit" to be repeated in this way, taking its cue from French customs. Just be sure not to make a habit of it, never to say it before your host does, and to avoid stopping by a friends table with nothing more than that to say.