It was installed in english... Some parts do display in English. I think it's only the Silverlight part that's in the wrong language because the menu and settings page etc are displayed correctly. Also, when I open the console on a server instead of a client PC it is displayed correctly. It definitley has something to do with the client's local installed languages.
By default, all client PC's are installed in french. In my case, I've set all language settings to english afterwards. The only thing that still displays in french is the windows boot screen, and altiris... This happens on all client PC's where I open altiris.