What would be the main differences in dialect?
Not to discourage other answers, but you might be interested in the relevant section of the FAQ on English accents, which includes the following:
What is the furthest year I can go back in time to England and be able to communicate with people?
Could a Middle English speaker and a Modern English speaker have been able to verbally communicate
If we could go back in time, who would be the first English monarch with whom modern English speakers could easily carry on a conversation?
When is the latest time I could've gone back knowing a modern language and still be able to communicate with people?
How far back in time can I go and still be able to communicate with English speakers relatively easy?
As a speaker of modern English, if I went back in time in England, how long until I wouldn't understand what the natives were saying?