If you are using a non-Steam version, you will need to replace the missing localization files manually.

This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later.

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Activision\Prototype 2

If you have a region-locked version (e.g., Russian) where the English files were completely stripped, you will need to find the lang or audio files online.