I figured out how to make the Twiddler "talk" and uploaded a demo video. The app is pretty simple. It listens for keyboard input and does one of two things, depending on the mode:
"Say Letters". It recites each letter you type. I use this to practice typing. Similar to Tutor except I can do so while walking.
"Say Words". It says the last typed word after you hit space, tab or enter.
I have tested it on an Android phone (Samsung S8) and on Mac OS. To speed up developing the prototype, I used Kivy so should work on other devices too. I'll post the code on GitHub soon and do a more detailed write-up on my blog site.
In the meantime, here's the video link: