According to a piece on Slate titled “Where Yinz At,” Pennsylvania is the nation’s most linguistically rich state.
A typical state, it says, maintains between two and three distinct, comprehensive dialects. Pennsylvania has five: Northeast Pennsylvania, Pennsylvania Dutch Country, Erie, Philadelphia and…well, yinz know the other one.
Pittsburgh and Philadelphia dialects get most of the attention, and the dichotomy is fascinating. As Carnegie Mellon linguistics professor Barbara Johnstone — probably the world’s foremost scholar of Pittsburghese — points out, there’s a horizontal dialect boundary across the state which roughly follows the path of Interstate 80, and the Allegheny Mountains bisect the state from the northeast to the southwest, isolating certain parts of the state and keeping others open to influences from other regions.
Pittsburghese, as you could probably guess, owes a great deal to the city’s mountainous isolation.