As my professor once said, "Modern English was invented in the year 1066 for Norman conquerors to pick up Saxon barmaids".
Some history. Old English was a Germanic language (or a loose confederation of Germanic languages), best remembered today for Beowulf. It is a well and truly foreign language for English speakers, as different as modern German is from modern English.
Then, in the year 1066, William the Conqueror invaded England from Normandy, and quickly conquered most of it. A trade patois formed almost instantaneously to facilitate communication between the Germanic-speaking English and the French-speaking Normans. This was Middle English. Unlike Old English, this is cleary English to modern speakers. A reasonably well educated English speaker can learn to read Middle English in a couple of weeks. "Translations" of Canterbury Tales can be found with the Middle English on one page, and a modern English translation on the other. (As an aside, I highly recommend Canterbury Tales. It's one of the most hilarious things I've ever read!) Middle English was the big step toward the messy, hodge-podge grammar and spelling we all know and perhaps love today.
The shift from Middle English to modern English took place during the reign of Henry VIII, famous for lopping off his wives' heads and establishing the Church of England (Henry VIII was the first monarch to reject Catholicism and embrace Protestantism, partly so he could get divorces and partly due to shifting power in Europe at this time due to technical innovations, but that's another story.). King Henry demanded that Oxford and Cambridge, the premier universities in England, start teaching in English rather than the Latin they had used for centuries. Professors were horrified. Give up the beauty and elegant perfection of Latin for that crappy trade patois the peasants use to sell fish and hurl insults? But they had no choice (Henry was, after all, fond of beheadings). So they did next best thing, which was to impose the beauty and consistency of Latin grammar on this crappy French-German trade patois.
("But didn't the Latin roots come from the Roman conquest of England?", some of you wonder out loud. No, it did not. Roman culture had little impact on England during their brief stay.)
One of the key results of this admittedly messy and violent history is that English is an extraordinarily flexible language. It is easy to learn a little, although a challenge to master. For all its terrible spelling, pronunciation, and grammar, English is very tolerant of error.
Another benefit is that English can and does absorb words from other languages, simply by mispronouncing them. Even grammar from other languages can be folded in. It still forms trade patois today - Creole, Chinglish, Spanglish, and other hybrids form whenever English encounters some less promiscuous language. Eventually, these work their way into the mainstream.
It's fascinating. You see disaster? You're welcome to learn Esperanto, a language scientifically designed to facilitate clean communication, that is spoken by no one but nerdy hobbyists. As for me, I'll be celebrating this glorious hot mess of a trade patois, a language that celebrates the complicated and always evolving nature of human cultures in its very bones.