Steam will automatically begin downloading the necessary English files (often several gigabytes). Method 2: Manual Installation of English Files
If all else fails, consider purchasing a region-free digital copy from a legitimate retailer that explicitly lists "Multilanguage" support. The Steam Gold Edition and Day Zero Edition both support English across all regions. Cod Advanced Warfare English Language Pack Download
A popular community "англофикатор" (English language pack) is available for Russian versions of the game. This file is approximately in size and has been downloaded extensively by players facing this exact issue. Cod Advanced Warfare English Language Pack Download