How far back in time could you go and still understand English?

If you had a time machine, how far back could you go and still understand English? AT what point in history would you not be able to understand the English language? If you went back in time to the 1800’s and 1700’s, you’d probably still be okay. This except is from the book ’Robinson Crusoe’, in 1719: “I, poor miserable Robinson Crusoe, being shipwrecked during a dreadful storm in the offing, came on shore on this dismal, unfortunate island, which I called “The Island of Despair” That’s fairly ea