This is the most common method. Advanced users on forums like CS.RIN.RU or Steam Community have extracted the English files from the global version of the game and uploaded them as a compressed archive (ZIP or RAR).
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Without this pack, you might be able to stumble through the multiplayer menus, but the nuanced story of Black Ops 2 —which relies on player choice and moral ambiguity—is completely lost. This is the most common method