Most of the hotel staff speak English. The waiters speak a little English. Depending on where in the city you're going, you might have some issues. In addition, most guest service staff speak English by default due to international (and mainly American) clientele.
The signs are in English, there are a lot of well-known food options, and you can usually pay for souvenirs and other unforeseen expenses with US dollars. At many resorts, it may seem like you're visiting another part of the United States that, by chance, has palm trees and a few touches of local colors or patterns in the decor. Resorts have to satisfy all tastes, so they will offer a variety of cuisines for everyone to enjoy. It's okay if you just want to relax at your all-inclusive resort throughout your trip, but there are actually plenty of things to do outside the resort as well.
In addition to all the food you can eat, all-inclusive resorts usually include all the alcoholic beverages you can drink. For those who aren't familiar, an all-inclusive resort is one where the vast majority of your expenses (accommodation, food and drink (including alcohol), some activities, and more, are included in the price of your vacation. Since there isn't much motivation to leave the resort (and, in fact, they encourage you to stay because you've already paid for all the services), tourists' money won't go to small businesses in the surrounding community. However, remember that, like any group of hotels, all-inclusive resorts aren't all the same.
Search for a resort you want to go to on Trip Advisor and, in fact, view the resort on YouTube. When I say all-inclusive, I'm referring to resorts that include food, drinks, accommodation and entertainment, all in one price.