Click here for an interesting web site on the Bairisch Language:
Actually, the Bairisch language exists only as an abstract general linguistic term for a multitude of dialects spoken in the above-mentioned regions. It is not a normalised standard language such as French or modern High German. At best, in the 17th and 18th centuries, there existed in the Bairisch language domain an official written language, which did more justice to Bairisch pronounciations than today's written High German.
Contrary to a widely held view, Bairisch is not a degenerate descendant of High German, but developed independently from Old-Bairisch (the Bairisch language in the Middle Ages). Despite is undisputed contribution to the formulation of modern High German, the septentrional German language planners, in creating the "DUDEN" (the official German dictionary), failed to consider many of its essential characteristics.