on Steam for all three game modes or manually copy the contents of the _Language Switcher/English folder into your main game directory. Do you need help finding the specific installation path for your version of the game?
The "Sound Bank Failed to Load cmn-root.english" error is almost always a handshake issue between Steam and your local files. By verifying your game cache and ensuring your Windows audio settings are capped at 48kHz, you should be back in the lobby in no time. black ops 2 sound bank failed to load cmn-root.english
If moving the language files doesn't work, try these secondary steps: on Steam for all three game modes or
If none of the above work, reinstall the game entirely, making sure to delete the sound folder before reinstalling. reinstall the game entirely