Open the folder Spellforce 2 in your Install directory, and run LanguageSelector.
There are 7 languages available: English, French, German, Spanish, Italian, Polish, and Russian.
Select the language required, and click "Download". The language pack download can be paused and resumed.
Once the download is complete, the language pack is installed to your game directory. A dialog window opens, indicating the installation was successfully configured.
You can now run the game, which will use the language selected.