"If you're stuck with a region-locked copy (like the Russian-only version), the 'English Language Pack' is usually a community-provided folder containing roughly 900MB of data.

: Some physical copies sold in Eastern Europe or Russia are hard-coded with specific languages and may not support an official English download. Steam Community or finding the exact on your PC? Depot 310343 - Advanced Warfare (Call of Duty - SteamDB

How English language packs are distributed