This post was the one I was looking for:

http://talk.maemo.org/showpost.php?p...2&postcount=38

- Install espeak.
- Install gstreamer-tools

http://maemo.org/packages/view/gstreamer-tools/

-> apt-get install gstreamer-tools

- X Terminal:
espeak -v de --stdout "Hallo Welt" |gst-launch -v fdsrc ! wavparse ! audioconvert!autoaudiosink

And it works! German voice.

Thanks for this great tip!