One of the common tv tropes in science fiction involving aliens is that the aliens all speak English. Some movies and tv shows throw in some lines about a universal translator (Star Trek), or a Timelord gift (Doctor Who) that the Doctor can share with others. If the aliens happen to come to Earth, they may claim to have learned our language from our transmissions. Others just gloss over it and expect to suspend our disbelief a little further. While this is often remarked upon, it tends to be an accepted part within the rules of the specific fictional universe.
Another common SFnal, trope concerns traveling to other timelines, or alternate histories. In these stories the protagonist is transported by means of technology, weird science, or magic to a world similar to ours, but where history worked out differently. Often enough the people there speak English, some idioms may be a bit different, but there's no significant difference in the language. This is rarely remarked upon, even though it should appear just as odd.
Language bears the marks of the history of its native speakers. In the short term, some popular culture will be different, so popular culture idioms and references will certainly be different. Over the long term, entire cultures may not interact in the same way. L. Sprague de Camp explored this concept in his story "The Wheels of If" originally published in 1940. The protagonist replaces his counterpart in an alternate timeline where history was different, part of the differences being that Latin never became an important influence over English, and Irish explorers discovered and settled America centuries earlier than in our history.
Dialog and some text quoted from newspapers are written in this Anglo-Saxon English. Camp created Anglo-Saxon words and expresisons to replace English words and expressions with Latin origins. For example, "airplanes" are "airwanes", "Indecent exposure" is "shameful outputting". "Reverend" is "Hallow". "To file a complaint" is "to mark in a slur". etc. Harry Turtledove wrote a sequel to the story a few years later, and he notes that he almost left in "second" and replaced it with "twoth"
While there certainly is a plot in the story beyond the language, figuring out the language, and in the newpaper quotes, the different spelling as well is a significant part of the story, just as significant as figuring out the culture, the protagonist's own role in that world and what he can do with his new life there.
The story has been reprinted in various collections, and it's very enjoyable.