Many players download the pack but still hear Russian. This is because the registry is locked.
Check the language pack under the "Add-ons" or "Manage installation" menu to install it. Troubleshooting Missing English Options Cod Mw3 English Language Pack Download --BEST
C:\Program Files (x86)\Steam\steamapps\common\Call of Duty Modern Warfare 3 Replace Files : Move downloaded files like localized_english_iw00.iwd Edit Config : Some versions require editing a localization.txt steam_settings file to say language=english Troubleshooting Many players download the pack but still hear Russian