Not to discourage answers, but this question has been asked alot
Here's the FAQ section on the English language and here's the FAQ on how far back you could go and still communicate
How far do I have to go before I can no longer have a conversation with someone and udnerstand them, using modern English
How far back in time could I go, and still be able to communicate with English-speaking folk of the day?
etc. Here're the search results
