I see, I gored your sacred cow.
It is well know that all the trades and professions had their private languages so they could discuss things and their customers did not know what they discussed.
Latin for the church and medical trades. Lawyers still have their arcane tongue.
Most of the others, butchers, tinkers, bakers etc had their trade language. I am from England and had a butcher and a baker in my family, and they told me bits of their language. True, it was not as comprehensive as English.
I also grew up in a Yiddish speaking family, as my father was a major on the Burma Road and we housed a family of displaced persons from Poland. Mother, Father, Bubba, and two young boys - all Jewish, and me and my Mom - I soaked up yiddish and by the time the war was over I could speak it as well as most kids of 9.
I used to startle the Jewish shop keepers, after WW2, when we emigrated to Canada, when this little Brit kid could know whatever they said. They were in the habit of carrying on conversations, secure in their privacy - Hah.
It stood me in good stead because I made many Jewish friends in Toronto in high school and college, because in those days there was a major barrier to many Jewish people in business circles. No brokers etc. This all changed in the mid 60's after a few prosecutions, and now it is wide open to all.
