By default, this is typically: C:\Program Files (x86)\Steam\steamapps\common\Call of Duty Advanced Warfare .
You can find the English language files on various modding sites and forums (such as CS.RIN.RU or dedicated PC gaming wikis). Look for a file usually labeled something like: Cod Advanced Warfare English Language Pack Download
This is the easiest method as the files are managed directly through the client: Steam Library Right-click on Call of Duty: Advanced Warfare Properties from the dropdown menu. Cod Advanced Warfare English Language Pack Download
If you're having trouble finding the official Activision website or prefer a more straightforward approach, you can also try the following methods: Cod Advanced Warfare English Language Pack Download