Hi Mattes,
Wow i'm jealous :-) I have a surface 1 pro which works with handwriting. But... here it is it only recognizes English so i have to write English to get the text converted. I do not select anything only if i want to convert a specific container of handwriting. On the Surface make sure your keyboard settings are important for converting. Click your keyboard in OneNote (little icon in the taskbar) and then the button bottom right (has a little keyboard on it) choose the various options to see if that works. Other languages? I don't think so.