A nice Atlas Obscura piece by Sarah Laskow on the history and psychology of American English, with discussions of Mencken and others:
English in America has always been different than the English spoken in the British metropole. In his 1992 book, A History of American English, the late linguist J.L. Dillard, who specialized in African American Vernacular English, demonstrates that the most originally American form of English was a pidgin, originating with sailor’s language. Early explorers of North America, he argues, would have used nautical pidgins and passed those on to native people. By the time the Pilgrims arrived in Massachusetts, there were people here—most famously the men the new arrivals called Samoset and Squanto—who already spoke a version of English that Puritans could understand.
But the English spoken by American settlers of European origin, too, quickly split off from the English spoken in Britain. At the beginning of the colonial period, America was a backwater. Not only was it distant from the cultural centers of Europe, it was far from the most happening place on this side of the Atlantic. So trends that surged in the language of London took longer to reach here, if they ever did.
It’s more correct to say, for instance, that people living in England developed a new accent than that Americans “lost” their British way of speaking. […]
What does American sound like today? There are some hints from the corpora that Davies put together: his Corpus of Historical American English contains 400 million words, drawn from sources from 1890 through 2009; his Corpus of Contemporary American English contains 450 million words, from texts, including soap operas, created from 1990-2012. With corpora this big and carefully constructed to draw consistently from a mix of popular and academic sources, linguists can look more carefully at how grammar and usage change over time. For instance, one hundred years ago, Americans would have said: “Have you any time?” “It’s very British, very old fashioned,” says Davies. Now, we would say: “Do you have any time?” We also might say: “You’re going to end up paying way too much for that book.” You’re going to end up—that construction wasn’t around 100 years ago.
Also, my wife and I are regular listeners to Fresh Air; having been annoyed a couple of weeks ago by a segment in which Terry Gross interviewed a speech pathologist who happily pathologized perfectly normal speech (hey, it’s what people pay her for) without any counterpoint from someone who knew linguistics, I was thrilled that for today’s show (the link has a transcript of excerpts as well as the audio file) she brought the pathologist back but this time sharing the air with an actual linguist, Stanford linguistics professor Penny Eckert (as well as journalist Jessica Grose, who has had to deal with people criticizing her voice). I was nodding so vigorously my wife said “You really like her, don’t you?” I said “It’s such a pleasure to listen to someone who knows what she’s talking about!” The poor pathologist clearly felt ganged up on, but that’s what you get when you’ve been selling astrological charts and then have to deal with an astronomer. It’s well worth a listen.