If you're visiting the Caribbean and you speak English, you're in luck: English is the first or second language in most Caribbean destinations and is the unofficial "language of tourism" as well. Having said that, however, you'll often find that your travels will be more richly rewarding if you can speak with the locals in their native language. In the Caribbean, that's usually determined by which colonial power -- England, France, Spain, or Holland -- held sway over the island first or longest:
English: Anguilla, Bahamas, Bermuda, Cayman Islands, British Virgin Islands, Antigua and Barbuda, Dominica, Barbados, Grenada, Trinidad and Tobago, Jamaica, St. Kitts and Nevis, St. Vincent and the Grenadines, Montserrat, St. Lucia, Turks and Caicos, U.S. Virgin Islands, Florida Keys
In addition, nearly every Caribbean island has its own local patois or creole that locals use primarily to speak to one another. In the Dutch Caribbean, for example, this language is called Papiamento. It's not uncommon to have island residents speak to each other in rapid-fire patois that can be unintelligible to unfamiliar ears, then turn around and address visitors in perfect schoolhouse English!