Iconic and "recognized" Worldwide - The Pirate "Accent" (or also known as "Pirate Speak), has been cemented into modern thought by virtue of hundreds of Hollywood movies and countless Television shows. The typical Swashbuckling Pirate is NOT complete with his "accent" of "Cockney English" - inclusive of "dropped letter H's" and a hearty "Arrgh". This is in no way accurate by a long shot! Pirates were (by no means), the lowest "rung" on the Social Ladder of Society (regardless of Era). This was true of any Seaman, actually. Coming from the poorer sections of Society conversely, a typical Pirate was likewise NOT the most educated of people.
However, Pirates and Privateers were NOT indicative of just England. Pirates came from all Countries. No doubt a "busy" Dock or Harbor such as Port Royal, Jamaica was full of many different languages and their related "accents" (all in their own poor grammer and speech, as well!). The "scourge" of "Pirate Speak" REALLY began with 19th Century, Scottish Writer Robert Louis Stevenson. Influenced in his own youth by both Daniel Defoe's "Robinson Caruso" and the "infamous" 1719 book by "Captain" Johnson "A General History of Pyrates", Stevenson wrote "Treasure Island" in 1881. Serialized as a 15-part story for a Boys Adventure Magazine - it was Stevenson who "created" not only the general "Pirate Language", but the endearing "image" of the "Peg Legged, Parrot on the shoulder, rum swilled , Pirate". In the 19th Century, "Sea Adventures" (not just Pirates), were "all the rage" throughout the World. Brought into the "Mainstream" Public view, Pirates became heavily romanticized. Pirates (although criminals), were (and are), firmly locked into Popular Culture as what Stevenson (and others), made them into - Anti-Heroes.
This leads us to "International Speak Like A Pirate Day" - celebrated on September 17th. An American "Goof" Custom born out a group of Pirate Enthusiasts, their 1995 "joke" came into National exposure (then International). Now whole "Chapters" of Pirate "speaking" people participate each year (and yes, using Stevenson's "Pirate Speak" and accent).