To change the language of the game you are playing:
- Open Steam and click on your Library tab.
- Locate the game you want to change the language for in your Game list.
- Right-click on the game name and select properties.
- Click on the language tab and select your desired language.
- Any language packs that need to be downloaded will then be done automatically.
- When you relaunch the game, it should play in the language you selected.