I've tried to find this out by myself, but the source material tends to be, well, let's say "comprehensive", and as I am no linguist it's very hard to find the details from the jungle of information. Furthermore I am not a native speaker of neither English nor German, and there isn't that much of stuff available in my mother tongue. I've studied German for six years and I am somewhat interested in the history of Prussia, so this is why I ended up here asking you. My teacher wasn't capable to give a satisfying answer.
Here's the question(s): what kind of German was spoken in Prussia during the 19th century? Were there great differences between the dialects of people of East Prussia and the Mark Brandenburg? How did it sound like? Did the spoken language differ a lot from the one used today, or was it relatively the same? How many Germans are there still remaining in the nowadays Polish territories, and does their dialect have anything in common with the language of the old days?
Thanks in advance.