Thanks, Tex, for all the useful links. I'll spend some time with them, I guess.
Meanwhile, here's a quickly assembled test epub for testing the features I am intersted in for the book I'm preparing right now:
- images as initials,
- ae- and oe-ligatures,
- words and phrases in French, Italian and German within an English text.
tts-test-epub3-corr.epub
Everybody feel free to run this through any TTS app you might have.