If you are trying to switch from Polish to English (or vice versa), the following manual fixes are often used by the community:
Save the file and restart your computer before launching the game. Method 2: Synchronizing the Steam Language Settings Black Ops 2 Sound Bank Failed To Load Cmn-root.polish
Paste the copied files here and choose "Replace files in destination" if prompted. 3. Change Steam Interface Language If you are trying to switch from Polish