I read something about how English was simplified as a result of the Viking invasion of England in the middle ages. It sounds like koineization. English might be weird, but it seems to be weird in a way that makes it highly exportable, like a successful product.
That's right. Old English has grammatical gender and noun cases (like modern German). Modern English retains case only for pronouns.
They were lost when the Danes invaded. The language was simplified to a mutually-understandable subset.
http://www.xibalba.demon.co.uk/jbr/ranto/
I see this was posted overnight in my time zone. Several of the earlier comments correctly point out that empirically, a language that has been acquired by many second-language speakers (for example, English) must not strike too many people as unlearnably "weird." Many widely spoken languages have undergone a process that linguists call "koineization" (after the spread of Koine Greek as a common language of the ancient eastern Mediterranean and Near East)
http://www.jstor.org/discover/10.2307/4167665?uid=3739736&ui...
http://www.lancs.ac.uk/fss/linguistics/staff/kerswill/pkpubs...
http://en.wikipedia.org/wiki/Koin%C3%A9_language
in which the language simplifies some grammatical (and possibly phonological) features as it is spoken by more second-language speakers for trade or for use as a language of national administration in a multilingual region.
The United States is largely an English-speaking country, but only about one-fourth of Americans have ancestors who spoke English before arrival in North America. (Indeed, only one of my four grandparents, all of whom were born in the United States, grew up in an English-speaking household.) In other words, General American English is a koine language of second-language learners of English, so it is not surprising that it is spreading all over the world.
P.S. Feel free to visit my user profile here on HN to see more about my background in linguistics and language learning and teaching.
AFTER EDIT: Cantonese versus Mandarin as "dialects" or "languages" were mentioned in other comments. Cantonese is at least as different from Modern Standard Chinese (Mandarin) as German is from English. How you might write the conversation
"Does he know how to speak Mandarin?
"No, he doesn't."
他會說普通話嗎？
他不會。
in Modern Standard Chinese characters contrasts with how you would write
"Does he know how to speak Cantonese?
"No, he doesn't."
佢識唔識講廣東話？
佢唔識。
in the Chinese characters used to write Cantonese. As will readily appear even to readers who don't know Chinese characters, many more words than "Mandarin" and "Cantonese" differ between those sentences in Chinese characters.