English is the most important language in the world for the conducting of trade. This language is a first language to people in the most developed economies in the world, including the US, Canada, Australia and the United Kingdom. The language is West Germanic in origin and shares many characteristics with modern German, Dutch and other languages that belong to that family. It is also an Indo-European language. This language developed in the UK and Scotland. It is among the most widely-read and spoken languages on the planet and, for those in the sciences, English proficiency is almost a requirement.
The English language also drives much of the technological sector. Programming languages, for instance, contain by and large English words where human-readable phrases are concerned. The language that makes the Internet what it is, HTML, is entirely English based. Words on a web page are designed and ornamented using phrases such as "bold", "underline" and so forth, making English familiarity a requirement for anyone in the technological sector, even if their job entails interacting with computers alone. This language is also widely used in medicine, along with Latin, which makes it a necessity for businesses that deal in healthcare.
English is also a popular language for treaties and other international documents. Passports usually have English text written on them. Even if you visit a country that isn't one where English is the majority or native language, there will usually be plenty of people who speak it as their second language. In many ways, English has evolved to become an almost universal language, a dream that led some people to create their own languages from whole cloth, to foster the convenience of communication that English offers to the world at present.
That being said, English is a very difficult language. It is full of borrowed words, has counterintuitive spellings and phrasings and the syntax is not particularly flexible. It takes expertise to translate documents from another language into English. English has strict conventions with word order, and the meaning of a sentence can be entirely shifted by a small error in punctuation or phraseology. Nevertheless, the spread of English across the world, largely by the influence of imperial powers who spoke the language, has made it one that is understood most anywhere. It is, by far, the most popular second language in the world and, in many ways, is a passport onto itself.