Many distributions are moving from espeak to espeak-ng, but gespeaker is not compatible with it, because espeak-ng uses /usr/share/espeak-ng-data/ instead of /usr/share/espeak-data/ in engines/engine-mbrola.py and engines/engine-espeak.py
The espeak-data data has been moved to espeak-ng-data to avoid conflicts with espeak. There have been various changes to the voice, dictionary and phoneme files that make them incompatible with espeak.
Many distributions are moving from espeak to espeak-ng, but gespeaker is not compatible with it, because espeak-ng uses
/usr/share/espeak-ng-data/
instead of/usr/share/espeak-data/
inengines/engine-mbrola.py
andengines/engine-espeak.py
https://github.com/espeak-ng/espeak-ng#espeak-compatibility
There might be other changes necessary.