When we say al fresco, we mean we are dining outside, at a picnic or in an outdoor cafe. When Italians say al fresco they are talking cool... cold, breezy, chilly, shady.... something they avoid at all costs. When they are fresco, they put on their puffy jackets and scarves. If you want a cold drink, ask "e fresca? Of course, you won't get it. Fresca also just means fresh, or room temperature.
If you see Prosciutto as an ingredient here in the States, it's very Italian... that fatty, paper-thin salt cured ham, usually from Parma. But in Italy prosciutto is just ham--any ham. When asking for what we call prosciutto in Italy, look for prosciutto crudo (raw), even though it's not exactly raw. Cooked ham is proscuitto cotto (cooked). For what it's worth, ask for Speck if you want to try a much drier, smoked prosciutto. Delizioso!
Then there are the English words that were re-invented by Italians. Italians don't go jogging, they go footing. If you want to rent a tuxedo in Italy, you really want to ask for a smoking. Yes, as in smoking jacket. And if you want to put your child into day care, you want to look for baby parking. Hopefully, not in a lot. After the kid is parked, and you want to go out to to a dance club, you want to find a night, I suppose, even if the club is open during the day. (Why not notte, the Italian word for night?) I guess that's better than the French calling a nightclubs a boîte (box). Which reminds me, in Italy you put your car into a box, not a garage. And your baby goes into a box too, not a playpen. Just don't get them mixed up.