How to install more voices for speech-dispatcher

Hello, I did browse few threads and web pages and I ended up with a configuration file that looks like this services.speechd.enable = true; ## ..... environment.systemPackages = with pkgs; [ ## .... speechd espeak-ng mbrola-voices mbrola ] I thought this is all the magic I need to make the mbrola voices available for my speech-dispatcher, but this is what I see with or without the mbrola-voices mbrola packages $ spd-say -O OUTPUT MODULES pico flite espeak-ng $ spd-say -L ...