History of the Polish language

The Polish language is a West Slavic language, and thus descends from Proto-Slavic, and more distantly from Proto-Indo-European; more specifically, it is a member of the Lechitic branch of the West Slavic languages, along with other languages spoken in areas within or close to the area of modern Poland: including Kashubian, Silesian, and the extinct Slovincian and Polabian. The separation of Polish as a language is conventionally dated at the second half of the 10th century, linked with the establishment of Polish statehood and the Christianization of Poland.

Source: Wikipedia — History of the Polish language (CC BY-SA 4.0)