How Far Back In Time Can You Go Before the English Language Becomes Incomprehensible

In October 2015, film production company Yestervid posited the question "How far back in time could you go and still understand English?" and then proceed to answer by using reverse chronology to find where the current iteration of the language drastically parted with the version of yore.

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 easy to understand, but you might struggle with old slang words like 'batty fang' and 'kickerapoo'.

via reddit