A long time ago, in a university far, far away, I began studying Japanese with a text that our well-meaning instructors told us was standard Japanese, the kind of Japanese that could be used anywhere in Japan.
My university had an exchange program with a Japanese university in the Osaka region. I was not to go to Japan until after graduation, but a student who participated in the program came back speaking a language that was quite unlike the textbook drills.
One memorable day shortly after his return, our class was asked by the prim and proper Tokyo-born Japanese instructor to ad-lib basic conversation. Fifteen years later, I still don't know what flowed from his mouth, but whatever it was, the student's non-standard reply infuriated the teacher. "That," she said in a quiet voice but with eyes flashing anger and surprise, "is not Japanese. That is Kansai dialect!"