I find many of these response amusing, in that many don't really know their history very well.
While the British Empire did spread the English language around the globe, it did not cause English to be an international language the way it is today. And many have forgotten that France, Spain, Portugal, and to a lesser extent Germany, all had empires that spanned the globe. In those colonies, the European colonial language ruled. The British Empire had little to do with the globalization of English in the late 20th and 21st centuries.
French was long the language of diplomacy and communications (as was pointed out by several) and was only supplanted by English in the mid 20th century. It was often the preferred second language for those who were sophisticated or of culture (or who wanted to be seen as such). It was not commonly spoken by ordinary people.
Latin was a global language for those in religion, science and education for many centuries. It began to die out as the Catholic Church broke apart with the Reformation, making it less popular amongst Protestants.
English only became a global language, spoken as a second language by people of all types all over the world after WWII. And not to sound conceited, it was because of the massive globalization of American culture, business and military. American military forces were all over the world, in bases or wars. Think Korea, Japan, Germany, Philippines, Middle East, parts of Africa, etc... Just about anyone that wants to do business in the world will have to deal with American businesses and practices. And American culture became a dominating force with TV, radio, music, internet... Even in places where governments were anti-American, like the Soviet Block, American music and culture were popular with common people. And as the internet became widespread across the globe, it furthered the spread of English, again largely due to American influence over it.
Also, the American tourist market was bigger than anything that had ever happened in history. People all over the world were exposed to Americans far beyond their exposure to other language speakers. That meant nascent tourist industries worldwide soon adapted to English, as Americans were their best customers.
A few have pointed out that "not everyone speaks English" and they are right. But anyone in the international business world, tourism, or that communicates online globally will likely speak English. And as more people adopted English to communicate with Americans, the more they find they can communicate with each other even if it has nothing to do with Americans. That means it is highly unlikely to be supplanted by another language, even if American global dominance wanes in the 21st century.
