While Plutonium is beloved by the community, it is third-party software. Always scan files and use at your own risk. The official method is always safer. Method 3: Manual File Swapping (Advanced) If you have a friend with the legitimate English version, the language files live in: \Call of Duty Black Ops II\zone\english \Call of Duty Black Ops II\sound\english
Unlike modern games that let you switch languages via a dropdown menu in properties, Black Ops 2 was released during a transitional period where language files were often locked to your game’s region code. You usually cannot simply download a 100MB "patch" to switch from French to English.
In this case, users used to rely on a specific fan-made launcher called the or "Plutonium" client. Plutonium T6 was a community project that not only restored dedicated servers but also allowed you to force the English language regardless of your registry key.