(I have never answered on this sub because I am not a historian, so I apologize if this answer is not appropriate and understand if it has to be deleted. I am answering now because I think I know enough to point OP in a direction.)

There are four major "timeframes" of the English language: Old English (~450-1050), Middle English (~1050-1450), Early Modern English (~1450-1700), and Modern English. You would not be able to understand Old English. The interesting thing about Middle English is that it was extremely diverse, so you might be able to understand enough to get along, depending on where the speaker was from. Look at the difference between The Canterbury Tales and Sir Gawain and the Green Knight. Assuming that most educated people would be able to understand Early Modern English with the exception of some vocabulary words, you might be able to go back to the late 1400s or maybe even mid-1400s in an area near London (where Chaucer was). I don't think they would understand you, though, so not sure about how well you would be able to actually communicate.

Baugh and Cable have a good history of English that is very interesting and discusses the influences on the language.

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