Well, he enrolled in the university to Bologna as member of the German Nation!
Nope, he was enrolled in the university of Bologna by his
Uncle as a member of German nation, there is no proof whatsoever that Kopernik thought of himself as German, he never wrote a single word in German, not one, every written word we have left is from him is in Latin except for letters to few German friends and associates who were not fluent in Latin, this alone speaks volumes if the guy uses his supposedly German language only if he has to.
As to why Kopernik didnt write in Polish? Because no one wrote in Polish (or few) the Polish language of science and literature at a time was Latin, add to this that the guy was fighting for the Polish king, commanding among other Polish forces in defence of Olsztyn (then Olstyn, before that Allenstein) and we get a pretty good idea of who Kopernik was.
He was half German ethnically of that there is no question but even during his life he chose his allegiance not to mention his father was Polish.
I doubt he spoke one word polish at all...no proof for that!
He was running several estates overseen by Poles and commanded troops from Mazovia where Latin was not popular so yeah given that he studied on a Polish univeristy and interacted with other Poles on a level that required fluent Polish its a pretty safe bet that he did.
Now whether he wrote in Polish its another matter, he did write to several oversees, commoners who wouldnt speak Latin or German but since those letters are not preserved the topic is open.
Mind you if you told Kopernik he was German or Polish he'd probably look at you in a funny way and tell you "i'm a subject of the Polish king" thats how it worked back there.
