I was reading recently a piece in my mother tongue (that isn't english) about its evolution through time. How words from different languages (even from European ones) were taken and adapted into words in my native language. I have also read many old works (some dating to 15th century CE) in my mother tongue and find some similarities with the modern version of the language, and I am sure I can make myself understood to an extent, should I happen to go back to the 15th Century.

Hence, I was curious on how it would work for English. The only really old works of english I have seen and read are plays by Shakespeare. I know that the spellings of lots of English words were different back then. But the language written in plays would hardly have been the same as spoken by common people, right ?

So I wanted to know just how far back in time would one have to go to find huge differences with the english we now speak to the extent that communication becomes practically impossible.

Really sorry for my shoddy English. I am also not sure if this question is suitable for this sub. Would be very glad to get pointed to other subreddits where I might find answers.

Thank you.