In a Course On Tape about the development of the English language I borrowed from our library, Stanford linguistics professor Seth Lerer described the great "vowel shift" in English that left us so many Shakespearean rhymes that are no longer rhymes (and turned clark to clerk, darby to derby, Hertford to Hartford and so on).
The professor said that in his class a student, hearing what the vowels used to sound like, described it as "pirate talk." Lerer said, in fact, that's what it was. Pirates' language came from the decades when English made that vowel shift, and that's one reason it sounds so distinctive to us. Shiver me timbers, me hardy! ("Me" was of course shifting to "my.")
Pirate author John Baur from http://www.wordsmith.org/ notes that our idea of Pirate talk comes from portrayal of Long John Silver by actor Robert Newton (above) in the 1950 Disney version of Treasure Island. Newton came from Cornwall, in Southwestern tip of England, and his distinctive Cornish accent is full of linguistic anachronisms.
avast (uh-VAST) interjection -- Stop (used as a command to stop or desist). [From Dutch hou vast (hold fast), from houd vast.]
false colors (fawls KUL-uhrs) noun -- Deceptive actions. [When ships approached each other at sea, sailors would look to the flag to determine whether the other vessel was from a friendly or enemy nation. They'd often try to confuse the other by flying a false flag until they were close enough to attack.]
Jolly Roger (JOL-ee ROJ-uhr) noun -- The pirates' flag, showing a white skull and crossbones on a black background. Also known as the blackjack or black flag.]
buccaneer (buk-uh-NEER) noun -- 1. An unscrupulous adventurer in politics, business, etc. 2. A pirate. [From French boucanier (buccaneer, barbecuer, hunter of wild ox), from boucan (a frame for smoking meat), from a French adaptation of a Carib Indian word bukan, a way of slow-cooking meat over a low fire on a grill.