There are two dutch voices: One is computer synthesized and that's what i think you mean. Then there is another natural female voice wich is nice and it should show up under Nederlands Mapfactor. When I newly installed the app it was'n there so i copied it from my old backup in the maps directory (sounds_nl.mca).
Yes the synthesized is the terrible one. Now i have finally installed the 12.0.5 free version on my SD so i do have to try it first, hopefully the female voice in there.