Which language was used for administration in the Grand Duchy of Lithuania?

In the Grand Duchy of Lithuania, the languages used for official administrative purposes were Ruthenian, Latin, and Polish.12

Ruthenian—an East Slavic language based largely on Belorussian—served as the de facto official language for legal and administrative matters for much of the state's history. However, Polish also played a significant role, eventually becoming the preferred language of the upper classes and the administration as the influence of Polish culture grew. In 1697, Polish officially replaced Ruthenian for administrative and legal purposes, a change that ratified the status quo already established among the nobility.12