In response to the question about real-world applications of Votrax:
My exposure to the Votrax was on a version of it (probably rather early -- 1977 I think)
that was a small box connected as an add-on peripheral to the PLATO system terminals. The
programming system included an API (set of TUTOR language commands) that effectively
provided a text-to-speech service.
At the time, text to speech for English was beyond the state of the art, or at least
beyond the skill level of the people involved in that project. But they did have useable
text to speech for German, Spanish, IPA (International Phonetic Alphabet) and Esperanto.
There also was a way to write English in a more phonetic manner that could then be spoken,
called "WES", I don't know what that stands for.
I saw a demo of this, it certainly worked. Pretty amusing to hear the computer say
"Auf den Autobahnen gibt es keine Geschwindigkeitsbegrenzungen." I don't
know if it was applied to any production applications ("lessons").
The software actually still exists, but it hasn't been revived. There is a CDC 6000
emulator that can run it, but the missing part is a Votrax emulation. Or an actual device
that could be hooked to a PC, I suppose.
paul