It's not the same as a regional dialect or accent. Consider it more like Romany; a language spoken by a societal subset that is intentionally designed to be confusing or unintelligible to outsiders. Cockney Rhyming Slang is a moderate version of it; you can listen to it for hours, but you're not going to suddenly 'get it' unless it's explained to you.
Other examples would be Polari, a language used by the homosexual community in the UK in the 1950's and 60's:
http://www.bbc.co.uk/dna/h2g2/A10357832
Or Nadsat, the invented language of the book "A Clockwork Orange," although that was fictional AND you could decipher it by reference.
American and UK Carnival workers (carnies) also have or had their own intentionally-encrypted language. The words are English, but their use of them is unfamiliar and cannot be deciphered by the uninitiated listener - this is by design. Some of this language persists in the age of professional wrestling. Notoriously, former Minnesota governor Jesse Ventura used it when he referred to politics as a 'work' which is wrestling slang for a set-piece battle, a game, a cheat, a foregone conclusion. Probably some of the most truthful words ever uttered about politics in America.