Geordie = A regional dialect. Basically anybody from Newcastle. In the US, you guys have 'Jersey Shore', we have 'Geordie Shore', if that gives you an idea of what kind of reputation Geordies have.
Posh = Upper Class, tends to sound quite snobby - probably one of the ways of speaking associated with the English over sees. Hitting in an arm chair with a top hat and monocle smoking a pipe.
This app seems like quite a funny idea, to be honest, I have trouble understand what Geordies are saying anyway. If I had a Doncaster -> Southern translator a couple of years back, I might have understand my old flatmate.