his father was from Cracow ... anyway
When we talk about language:
Polish language in writing was created by Mikołaj Rej (1505-1569)
"Mikołaj Rej or Mikołaj Rey (Nicholas Rey) of Nagłowice, Poland. He is considered, along with Biernat of Lublin and Jan Kochanowski, to be one of the founders of Polish literary language and literature."
"A niechaj narodowie wżdy postronni znają,
iż Polacy nie gęsi, iż swój język mają."
("Let it by all and sundry foreign nations be known
that Poles speak not Anserine but a tongue of their own.")
Most people in Poland were writing in Latin in Kopernik's times.