With Brandenburg there was always struggling and warfare as Brandenburg sought to integrate the duchy of Pomerania within its realm she also claimed Pomerania inheritance as a whole and Uckermark in specific throughout history  despite she would not succeed getting the whole duchy of Pom until the last Griffin died heirless Brandenburg eg advanced into and temporarily incorporatet Stargard and most of Uckermark There were a lot of treaties of Pomeranian dukes against Brandenburg or other threatening neighbors like Mecklenburg The HREs central authority most of the time was very limited armed and diplomatic conflicts between the HREs statesduchiesprincipalities were common until Prussia succeeded to create a much or less unified centralistic Germany under its hegemony in late modern times   But in our case alliances as the one you mentioned are not suitable for determing the language used in the duchy Please dont have your editwar continued as it really makes no sense to deny historical facts that can be studied with a low amount of time and means Please inform yourself before further false edits are made  Maybe you are confusing the duchy of Pom with Pomerelia I really dont know what else I can do to get you study a bit of Pomeranian history which would pretend you from making false edits