To begin with, it is interesting to know that according to the Instituto Cervantes' study, there is actually more Spanish speakers in the USA than in Spain itself. Wow!
With more than 40 million native speakers and 11 million bilinguals (mostly children of Spanish-speaking immigrants), the USA is, in fact, the world's second largest Spanish-speaking country, right after Mexico.
For real facts, according to the US Census Office estimates, the USA will become the largest Spanish-speaking country by 2050 with around 138 million of speakers, that means approx. 1 in 3 Americans (and not counting on any Wall building).
Status of the Spanish language in the USA
Since 1980, the number of Spanish-speakers in the US has almost quadrupled in absolute numbers, while their share of the population went from 5 to 13%. Most Spanish-speakers are concentrated in states bordering with Mexico (California, Arizona, New Mexico, Texas) and the havens for immigrants on the East coast, mainly Florida, New York, New Jersey and Massachusetts. However, it's the long history of Mexicans vs. Americans as well as the general immigration that puts Spanish into its current standing. The USA do not have any language constituted as an Official Language, although the most dominant working language used by institutions is obviously English, and on top of that the American version. In states with a large distribution of Spanish speakers, such as New Mexico or California, official documents are issued bilingually. The exception is Puerto Rico, which, despite being part of the US Commonwealth, uses Spanish as the official primary language.
US Spanish dialects
Spanish used around in the US can be distinguished by dialects and origin, mainly Mexican, Caribbean and Central American Spanish. The English language influenced the Spanish used in the US (and vice versa), while it is quite common for the Latino community to mix Spanish and English, resulting in a fusion called Spanglish (popular mainly among younger generations). The environment is also a factor here, while the US Spanish-speakers tend to color the language with local US English accents and convenient English words thrown in.
Spanish is also by far the most common foreign language included in American school plans from elementary schools up to university level, and with following generations of Spanish-speaking immigrants, there is a strong will to preserve the background and speech of Spanish language.
Translation into Spanish for the U.S.
Is there a need to translate into Spanish for residents in the United States? Probably not. There are so many Spanish "languages", all with their flavors and idiosyncrasies. Standard Spanish is understood by just about any Spanish adept around the world, for Spanish in the USA, Mexican Spanish with a dash of American words are probably acceptable for local incentives.
Addressing a population of millions of speakers will require "standard" Latin American Spanish. We are all ears on this. After all, in the translation industry, we have so many flavors of Spanish on the American side. Everyone understand each other, but somebody chose to chop up American Spanish into ethnic groups, each with their own language code.
Today this is overwhelming, and there should be no need to serve local Spanish flavors to the Americas.