Check the /pc/ directory in your installation folder. Look for folders like sds_en (English), sds_fr (French), etc..

This massive overhaul includes restored content. If you download it from Nexus Mods , ensure you select the English Version specifically. Installing the Russian version on an English game base—or vice versa—will cause the game to crash.

If the game remains stuck in a different language despite library settings, you may need to edit internal configuration files manually: Mafia II: Definitive Edition - GOG SUPPORT CENTER