Almost all Americans speak English. Most Americans speak in accents that are recognizably similar to one another and to one traditionally associated with the Midwest, which was popularized in the 20th century by American radio, TV and movies. Although many Americans can discern differences between quite a few accents, the ones most likely to be heard as distinctive by foreign visitors include those commonly spoken in the South and Texas, the Boston area, the New York City area, the upper Midwest and Hawaii.
Many African-Americans and some other Americans also speak African-American Vernacular English (AAVE), which has somewhat different grammar and vocabulary than styles of American English usually regarded as standard. AAVE has had a great effect on more general American slang and colloquial language, in particular. Never assume that just because a person is black, s/he will speak AAVE, in particular because many immigrants from Africa or the Caribbean or their descendants cannot speak it, and also be aware that many African-Americans can switch back and forth between AAVE and standard American English effortlessly. Spanglish — an admixture of Spanish and English — is similarly commonplace in many areas with large Hispanic populations, and code-switching between Spanglish and standard American English is similarly commonplace.
Visitors are generally expected to speak and understand English. While many Americans study a foreign language in school (overwhelmingly Spanish followed by French), it is best to assume that the average person has not advanced far beyond the basics. Popular tourist sites often have signs and information available in other languages. Americans have a long history of immigration and are very accommodating towards foreign accents, and will sometimes take the effort to help you by speaking in a more standard accent.
American English differs somewhat from the English spoken in other parts of the English speaking world. These differences are mostly minor, and primarily around minor spelling differences as well as pronunciation. See the article on English language varieties for a detailed discussion.
Spanish is the first language of Puerto Rico and a large minority of residents on the mainland (with the fifth-largest Spanish speaking population in the world). Spanish speakers in the United States are often Puerto Ricans or first- and second-generation immigrants from Latin America. As a result, the Spanish spoken is almost invariably a Latin American dialect. Spanish is the primary second language in many parts of the United States such as California, the Southwest, Texas, Florida, and the metropolitan areas of Chicago and New York City. Many of these areas have Spanish-language radio and television stations, with local, national and Mexican programs. Most publications from the federal government, as well as some state and municipal governments are available in Spanish. Many establishments and government offices in major commercial and tourist areas have Spanish-speaking staff on duty, and it is possible with some difficulty to get by in the major cities and tourist attractions speaking only Spanish.
French is the primary second language in rural areas near the border with Quebec, in some areas of Louisiana, and among some African immigrants, but is not widespread elsewhere. In southern Florida, Haitian immigrants primarily speak Haitian Creole, a separate language derived from French, although a substantial number also speak French.
Thanks to the North American Free Trade Agreement, some products now have trilingual packaging in English, Spanish, and French for sale throughout the entire trade bloc, especially household cleaning products and small electric appliances. However, the vast majority of consumer products are labeled only in English, meaning that a rudimentary grasp of English is essential for shopping.
Hawaiian is the native language of Hawaii and Hawaiian Pidgin, a mixture of English, Hawaiian, Portuguese, Cantonese and several other languages, is also spoken by many people born in Hawaii. However, English is the most widely spoken language in Hawaii, and Japanese is also widely spoken there.
In the various Chinatowns in major cities, Cantonese and Mandarin are common. Smaller immigrant groups also sometimes form their own pockets of shared language, including Russian, Italian, Greek, Arabic, Tagalog, Korean, Vietnamese, and others. Chicago, for instance, is the city with the second largest ethnic Polish population in the world, behind Warsaw (although most Chicago-area Poles are American-born and speak only English). The Amish, who have lived in Pennsylvania and Ohio for generations, speak a dialect of German.
Some Native Americans speak their respective native languages, especially on reservations in the west. However, despite efforts to revive them, many Native American languages are endangered, and people who speak them as their first language are few and far between. Navajo speakers in Arizona and New Mexico are an exception to this, but even a clear majority among them speak and understand English too.
Bottom line: unless you're certain you'll be in an area populated by recent immigrants, traveling in the United States without a firm grasp of English is a significant challenge.
American Sign Language, or ASL is the dominant sign language in the United States. When events are interpreted, they will be interpreted in ASL. Users of French Sign Language and other related languages may find ASL intelligible, as they share much vocabulary, but users of Japanese Sign Language, British Sign Language, or Auslan will not. Closed-captioning on television is widespread, but far from ubiquitous. Many theaters offer FM loops or other assistive listening devices, but captioning and interpreters are rarer.
For the blind, many signs and displays include Braille transcriptions of the printed English. Larger restaurant chains, museums, and parks may offer Braille menus and guidebooks, but you'll likely have to ask for them.