Search for all files containing your current language name (e.g., "polish") and rename them to "english".
The path is usually: C:\Program Files (x86)\Steam\steamapps\common\Call of Duty Black Ops II . call of duty black ops 2 english patch install
Copy and paste the localized_english_iw07.iwd file from your patch into this folder. Go to the sound folder within your game directory. Search for all files containing your current language