"In Bristol, every day is talk like a pirate day"
Trad.
Basic Information
Traditional - not to say cliched - depictions of pirates, usually have them speaking in a strong, distinctive accent. For non-native English speakers, this is "talking like a pirate" … to the English, this is a West Country accent (typical of the South-West of England … including Cornwall for these purposes). Obviously not all pirates are from South West England - and one of the most famous (Henry Morgan) was actually Welsh - but this trope does have some historical justification.
Specifically, the key to this is that most popular portrayals of pirates focus on the Golden Age of Piracy in the Caribbean - and the main English port serving the Caribbean trade (and, it must be said, the Triangular Trade touching at the Caribbean) was Bristol … which is located in the South West of England and where, as per the flavour text, every day seems to be talk like a pirate day (everywhere else that is confined to the 19th of September).
This may still be somewhat anachronistic as the evolution of English means that what was spoken during the Golden Age would sound very different to anything spoken today (recall that the age began only a few decades after the age of Shakespeare).