Go to the SoundData\PC folder and delete all non-English language packs (e.g., Russian) while keeping English and SFX files.
Delete the localization.lang file in the main directory; some versions will automatically regenerate it in English if other language files are missing. Official Ubisoft and Steam Support assassin 39-s creed syndicate localization.lang english
Copy this file and paste it into the main game directory, replacing the existing one. Go to the SoundData\PC folder and delete all