That is if I had a conversational grasp of whatever language I needed, how far back in time could I go and still expect to be understood? I’m guessing we know and understand some pretty old languages in written form but how certain are we that we know how to pronounce them? And what languages are they?
If you went back 500 years, you would have some difficulty understanding what people were saying. It might take a couple of weeks to understand them well. If you went back 1000 years, you probably wouldn’t be able to understand them. It would sound to you like a weird dialect where you would every once in a while understand a word, but you couldn’t make out most conversations. You could probably slowly get used to it, but it would take you months of learning new words and grammatical patterns and ways of pronouncing things. If you went back 2000 years, it would be like a completely different language. You could learn it, just as you could learn any other language, but it would take years.
As for your other questions, they have rather complicated answers. Perhaps you should buy or borrow some books on linguistics. It would be simpler than trying to answer your question here.
This is going to depend on the language concerned, surely, since some languages have evolved faster than others?
To some extent, since some languages at some points have evolved faster than other languages at other times. Still, there are no languages that stay the same for any significant period. There are no languages that evolve so fast that by the time a speaker is old, they can’t understand young speakers.
It depends on the language. When it comes to Roman Latin, for example, you could easily learn it and pronounce it correctly.
Latin Pronunciation Demystified
For example, “Language teaching was big business in Roman times, and ancient Roman grammarians give us surprisingly detailed information about the sounds of the language.”
And… “transcriptions into other writing systems, such as Greek and Sanskrit, often pin
down the ancient pronunciation of Latin very precisely.”
Yes. But I have read that Icelanders, for example, can easily read Icelandic texts from the tenth century, whereas the typical English speaker will struggle with anything from before the fifteenth century. No doubt if a modern Icelander were transported back a thousand years there’d be significant pronunciation differences, but I image he’d pick those up fairly quickly. There would probably also be some spelling differences but, in spoken language, these don’t matter. There’d have to be some voculabulary differences, if only because the range of things people need names for will have changed in the space of a thousand years. But the grammar, the syntax and much of the vocabulary would all be completely familiar.
A nice example is Afrikaans, which was originally Dutch. A person speaking Afrikaans would have some trouble getting used to Dutch and vice versa. I’m a Dutch native speaker, but whenever I hear Afrikaans on the TV, I really need the translation to understand what is going on. And these two languages have only been diverging for the past 400 years or so.
UDS writes:
> . . . Icelanders, for example, can easily read Icelandic texts from the tenth
> century . . .
This is a common legend. It’s not accurate. What’s true is that speakers of Icelandic can understand the sagas (from about 800 years ago) approximately the way that English speakers can understand Shakespeare (from about 400 years ago). To understand Shakespeare well, we expect to have the spelling modernized. We read it and pronounce it in our mind in a modern accent that doesn’t sound much like the accent of Shakespeare’s day. We understand Shakespeare better if there are footnotes explaining the definition of some of the words. The same is true of Icelanders reading the sagas. The spelling is modernized. They mentally read it with a modern accent. They need an occasional footnote. So perhaps Icelandic has been changing half as fast as English over that period. You need to be very careful about modern speakers’ claims about how they can read older texts. Often it’s a matter of national pride to show that they haven’t changed much.
I’m not so sure on that. If you put a 80 year old in a group of teens, how much would they understand? There are always new slang words being invented and words are changing their meaning all the time.
Not many older people would know what “phat”, “bae” or “turnt” means. Most older people would also have different meanings for words like “shade”, “slay” or “ship”.
When I said was that it can’t be true that old people are unable to understand young people, I meant that the language can’t have evolved so far that there would be complete lack of understanding. Yes, of course there will be new slang all the time. That doesn’t mean that there is a substantial level of misunderstanding of young people’s speech by old people. What really happens is that a young person will occasionally use a new word that an older person has to ask for the meaning of, and an old person will use a word that has largely disappeared in use in recent years that the young person has to ask about. The claim that this is substantial misunderstanding is simply wrong. Indeed, the older people eventually learn to use the new words themselves, although they pick them up a little slower. Incidentally, the word “phat” has been around for more than 50 years.
I find that picking up new words that younger people are using is actually less trouble than learning other dialects of English. When I moved to England for three years, I found that I had to learn new words frequently at first and had to get accustomed to new pronunciations. This was a little difficult at first, but I soon got used to it. It was somewhat more difficult for me then as a speaker of Standard American English to learn to understand Standard British English than it now is for me to understand people who are fifty years younger than me.
Actualie, ye olden spelinge is not a significant barriere to vnderstanding. I have a copy of the Authorised Bible of King Iames with ye originall spellinge and it is not hard to vnderstand. Ye can learne to read it quicklie if you lerne the conventiones.
Two languages that have famously undergone major changes in the past 100-150 years are Japanese and Turkish, meaning that many native speakers today who were born in the 20th century often have a great deal of difficulty reading works written in the 1800’s. I was told by a Turkish language teacher that the problem in Turkish is considered serious because of the cultural disconnect that it has produced, with people unable to read the writings of their ancestors. Imagine if the oldest untranslated books that you could read were ones written in the 1930’s. Imagine no Shakespeare, no Mark Twain, not even the Gettysburg Address or the US Constitution - they would be in a foreign language to you.
By contrast, formal English writing has changed very little since 1850. Pick up a copy of Little Women or Tom Sawyer and try to read it. The biggest challenges to understanding are cultural and technological barriers for which you simply need to understand the time period in order to figure out what is going on. The language isn’t a barrier - it’s Modern English, plain and simple.
As above, from the : Not hard at all. From the 1611 King James Version
Bingo, you got it. All you need to do is learn a few basic spelling conventions that have changed since 1611 and you are ready to go.
One of the big ones is that in 1611, the letters v and u on one hand and the letters i and j on the other were not considered distinct, and the correct one to use depended on the position in the word. For example, live was spelled “liue”, and “unto” was spelled “vnto” (though “very” would still have started with a v, since it is word-initial).
There were also a few vocabulary updates made in the KJV, some of them being mentioned here. Perhaps Ralph Wiggum shouldn’t have been considered as failing English, but only someone whose language was a bit antiquated.
But Chaucer, 300 odd years earlier is a little more difficult:
Beowolf, 300 years before that, becomes unreadable.
Really depends. Shakespeare was considered to have spoken Modern English, and while the language in his plays maybe flowery, the words aren’t foreign. Middle English would be a bit more troublesome, try to imagine the thickest accent you can and that might help. Spelling in Middle English was a bit weird though, so I wouldn’t bother with it.
Old English might as well have been a different language. The vowels were often different and from region to region, dialects could vary drastically. You can find a few good sample texts online which are mostly West Saxon, but I can give you a few examples of what it looked like compared to modern English.
I’m not going to look up the actual text, I’ll try to copy it from memory, so there might be a few errors, but I’ll try my best to show you what the Lord’s Prayer looked like in Old English:
Fæder Ure,
þu þe eart on heofonum
Si þin nama gehalgod
Tobecume þin rice,
gewurþe þin willa on eorþan swa swa on heofonum
Ure gedæghwamlican hlaf sylle us todæg,
And forgyf us ure gyltas swa swa we forgyfaþ urum gyltendum
And ne gelead þu us on costnunge, ac alys us of yfel.
Soþlice.
Right, so we can see that it looks pretty foreign. Old English is a lot closer to Old German than modern English is, and that might be more obvious here.
I hope you know the Lord’s prayer, but I’ll offer a version of the above in a modernized way using descendant words:
Father [of] Ours,
Thou that art in [the] heavens,
Be thine name hallowed,
Become thine reich (rice related to the word riches, or German reich; meaning kingdom; wealth; area of influence),
Worth (make; bring into existence; give value to) thine will on [the] Earth as also on [the] Heavens,
Our daily loaf, sell (give) us today,
And forgive us our guilts as also we forgiveth our guiltors,
And not lead thou us in costning (related to the word “cost”, meaning basically temptation), but alese us of Evil
Soothly.
So you can see that while a lot of modern words are descended from Old English, the grammar and spelling are quite different and if I didn’t tell you what it meant, you would probably have a great deal of trouble understanding it.
I should note the pronunciation changes-
the letter “h” was pronounced as we do today at the beginning of words but as the “ch” in the scottish “loch” anywhere else in the word. The letter “g” sometimes sounded as the modern one, but more often as a softer “y” consonant sound. The digraphs “th”, “sh”, “ch” didn’t exist, and instead were replaced with letters like þ (thorn) or eth (although I can’t remember the ALT code for eth), “sc” made the modern “sh” sound, and “ce” made the modern “ch” sound. I could try to write the above old english in a way that you might be able to pronounce it better as a modern English reader:
Fah-der Oo-reh,
Thoo thay art on Heh-ove-oh-num,
Sih theen na-ma yeh-hahl-god
Toh-beh-coo-muh theen reech-(e)
yeh-werth-uh theen weel-luh on Eh-orth-an swah swah on Heh-ove-oh-num.
Oo-reh yeh-dahych-wahm-lee-can hlahv sool-leh oos toh-dahy
Ond for-yoof oos oo-reh yool-tas swah swah way for-yoof-ath oo-rum yool-ten-dum
Ond ney yeh-leh-ad thoo oos on cost-nun(g/y)-eh, ak a-loose oos ov oo-vel.
Soh-thleech-eh
Now that I think about it, the “y” vowel might be more similar to the “eu” used in some french words, like “jeune”.
Or search for other threads here on this subject. We do this at least once every year. In fact, if you find the earliest threads, you might not even be able to understand them! 
But to a modern reader, wouldn’t the King James would look like this?
(actually, would the silent ‘e’ at the end of darkness lead to a double long s, or a long plus short s?)
Not that this fubftantially changes the point that it’s moftly readable with minor effort.