Let’s say I were (a) in London and (b) had a functioning time machine. I am fluent in modern English (American) and no other language.
How far back could I go and still converse with the locals? I figure 400 years, but probably not 500. I can only read Chaucer in translation.
By contrast, how far back in time could a modern Greek/Italian/Hindustani/Mandarin/Swedish speaker go back (in a city where some form of their language has been dominant since time imemorial) and still understand the local language? What language has stayed closest to its ancient forms through the ages? Is there a pure strain of Indo-European spoken somewhere in central Asia?
The big question is how much effort you’re willing to put into it. If everyone involved is making an effort to speak slowly and clearly, with frequent pauses for “What do you mean?” and “I don’t understand”, you could go back a lot further than if your goal is a glib, uninterrupted colloquie.
And am I the only one who hoped this thread would be about the complexity of tenses necessesitated by time travel?
Icelandic is considered one of the most stable languages out there; it’s unchanged for over 1000 years (when Poul Anderson sent a protagonist back that far, he had him fluent in Icelandic).
By contrast, a thousand years ago, English was Old English and not easily intelligible, though quite a few of the words would be readable (“And” would be spelled the same, for instance, but would be pronounced “ond.”)
I seem to recall that written Chinese has been very stable, too, though the pronunciation has changed considerably.
And, no, there is no pure strain of Proto-Indo_European around today.
The fact that you’re in London influences the answer.
In recent times we’re accustomed to having a standard set of rules for the English language. Those rules were codified by various sources, over the last 200 or so years. Before that time, there was no standardization; no universal dictionaries, grammar guides or anything else. Consequently dialects could vary quite a bit, even within the English-speaking world. Vocabulary, grammar, diction and spelling were all over the place, depending on where you were in England (or Scotland, America, Canada, etc…)
When self-designated authorites decided to standardize and formalize the language, it was the urbanites who took the lead. Specifically the publishing houses in London produced a good chunk of the original books on grammar. Consequently, what became ‘standard English’ is most closely related to the London dialect of English. Of course Shakespeare helped to spread London dialect as well, since he was always the most widely read English-language author.