A: Yes. Simply repeat the Steam/console steps and select your original language. Steam will re-download those files (and may remove English ones to save space).
Markus checked his game’s SteamDB page. Sure enough, his key was for the “DE/AT/CH” region (Germany, Austria, Switzerland), which only included German and French audio. English was not available for that product ID. Call Of Duty Advanced Warfare English Language Pack Free
Select the game again to see available files and check if English language data is listed as an uninstalled add-on. A: Yes
Should I continue the story with a high-octane at the Atlas facility, or focus on a stealth-heavy escape through the ruins? Markus checked his game’s SteamDB page
For more official help, you can visit the Activision Support page or check the Steam Community guides. Guide :: Changing the language to English - Steam Community