This is critical. If you mess up the registry, you might have to re-download 7GB of data.
Depending on your platform, you can typically enable English through the game's properties: Ubisoft Connect (PC): Go to your library and select Tom Clancy's Splinter Cell: Conviction on the right side, then choose Properties tab, select from the language selection section. ubisoft splinter cell conviction english language pack
PC / Xbox 360 Review Focus: Localization quality, voice acting, script adaptation, and technical clarity. This is critical