Sad, but true. For whatever reason (culturocentrism, intellectual laziness), Americans assume that English is the lingua franca in which people from other countries surely must be fluent. Hence the stereotype of the Ugly American -- innate arrogance and a failure (or refusal) to understand local culture. As it happens, one can get by in Europe using only English, because citizens of the EU countries tend to be multilingual, and also because English has become the de facto language of international business, just as it is the default language in aviation.
However, our complaisance is misplaced, and potentially harmful. Savvy people recognize that not only is learning two or more languages an excellent way to improve one's mental acuity, it is also a vital bridge toward making new friends, new business contacts, and learning to understand and enjoy the rich cultural diversity that exists not just globally, but locally as well. Nicholas Kristoff writes in Primero Hay Que Aprender Espanol about "the paramount importance for our children of learning Spanish .... Spanish may not be as prestigious as Mandarin, but it's an everyday presence in the United States. Hispanics made up 16 percent of America's population in 2009, but that is forecast to surge to 29 percent by 2050, according to estimates by the Pew Research Center. (The map below shows Spanish-speaking households as of the 2000 census.)