|Blackbeard the Pirate Engraving, Benjamin Cole, ca. 1724|
Arrr Matey! The Origins of the Pirate Accent A strong case for the origin of pirate talk.
Pirate R As In I R Eland? This is a potential alternate explanation to the link above.
West Country Dialects A comprehensive resource on speech in Southwest England.
Bristol Dialect/Glossary A focused look at words and phrases from a Southwest England county.
Sid Totter (b. 1877): Listen to him speak in a 1950's West Country dialect.
And here is Robert Newton, a.k.a. Long John Silver, displaying his Dorset accent in a reading of a short poem:
And here is Newton as Long John Silver:
Not sure I care much about the origins after hearing Newton's performance again. I was six years-old when he appeared in Walt Disney's Treasure Island (1950). He'll always be my personification of the perfect pirate, me hearties.