Now, because the app takes the same language as my phone, it's in English. However, I've got a Dutch voice installed, and everytime I open the app, TomTom now warns me that it's not compatible and no voice instructions are given during my commutes. So I don't necessarily need an option to change the app language, if I can just choose the voice language that I want.
This is a very basic function which even free apps have.
Thanks, Koen Christiaens!