George,
It is a pity, the languages for voice are made by Microsoft in 1985 style of deployment. They are completely depending from the Microsoft OS you are using (not framework).
Therefore your OS makes how the speaksystem works. In Windows 10 there are even included voices completely separated for Cortana and .Net (The cortana ones can then be installed using a System Settings, while the .Net ways have to be installed using the
language packs which you can install, if youdeinstall then direct the voices stay).
A pity is that it seems that every department of Microsoft seems to use their own speech system so it is almost impossible to find on Internet documentation which does not conflict with itself, likewise the experience you had.
Therefore tell at least the OS you are using.
Success
Cor