I learned German in order to read church records pertaining to my Moravian and Dutch Reformed ancestors. These records were from the 15th, 16th, 17th and 18th centuries, both in the British colonies of Pennsylvania and North Carolina, and earlier in the Palatinate, Pfalz, Alsace, Canton Basel, Wurms and der Schwarzwald. I had no difficulty in reading these records at all, and I was taught Hoch-Deutsch.
It was more of a standardization of dialect than anything else, which coalesced as a result of Martin Luther’s German Bible, much as Tyndale and the subsequent and in many ways derived King James Version coalesced and standardized English.
Thanks for that knowledge. FR is a great place to learn.