The "pirate accent", its origins, and cultural signifiance
Mostly an invention of 19th-century adventure novels and early-20th-century swashbuckling movies
These were often written for children, or it was expected that children would be among the readership, and polite society in Victorian times pretty much required bowdlerization anyway.
Real pirates wouldn't call you a "scurvy sea-dog" or a "land-lubber scallywag", they'd curse you out just as any other criminal in the midst of terrorizing you would.
Notably Treasure Island (written by a Scotsman), and the Disney version of it in the 1950s.