One superficial and misguided statement that you routinely hear in large monolingual countries such as the US and Brazil is that a common language is an almost necessary condition for economic progress. The idea will usually be presented attached to silly examples such as "look at poor India, they have to deal with so many languages, for sure it's one of the main reasons why they are so poor," or "look at the European Union, such a political mess, they speak too many languages."
My reaction is always to point out that one of the most developed nations in the world, according to any standard of choice, Switzerland, is a small country with four official languages. Most rich nations are found in Europe despite its Babelic network of languages. And you can find many examples of large but mostly monolingual nations and regions such as Brazil that didn't do nearly as well as their Babelic peers.
Victor Ginsburgh presents the point scientifically in this interesting article and uses the opportunity to make fun of a recent demonstration by Harvard's Larry Summers of typical monoglotic arrogance:
In 2005, Larry Summers, then President of Harvard University, outraged 50% of the world by claiming that women are not as talented as men in science and mathematics. This time, he has outraged some 94% of the world’s population by suggesting that native speakers of English should forego learning other languages since, anyway, the rest of the world will soon become fluent in English (Summers 2012). ... However, and interestingly enough, Melitz ... shows that English as an OCC is no more effective than other European languages in promoting trade.