Ensure the "localization.txt" file in the root folder is edited to say "english" instead of the previous language.
How to Download and Install the English Language Pack for CoD: Advanced Warfare For Steam Users Call Of Duty Advanced Warfare Language Pack English BEST
If the game does not automatically switch, check the Manage Game Content or Ready to Install section. Ensure the "localization
Update Drivers: Ensure your GPU drivers are current, as language updates can sometimes trigger minor configuration resets. Call Of Duty Advanced Warfare Language Pack English BEST
Verify Game Files: If the game crashes after a language swap, use the "Verify Integrity of Game Files" tool on Steam to repair corrupted data.
On consoles, language support is often tied to your system settings or the region of the store where the game was purchased.