If your launcher automatically updates or verifies game files, it may delete the custom English files. To prevent this:
Right-click Far Cry 3 → Properties → Language → Select English. Steam will download only the missing voice files. This is the safest method, but only works if your license is multi-language. English Language Pack For Far Cry 3
Close Far Cry 3 and shut down your game launcher (Steam or Ubisoft Connect). Open the downloaded English Language Pack folder. If your launcher automatically updates or verifies game