For my native language, Norwegian, Piper TTS is at best "usable", and sometimes a fair bit worse than that. At least in its default form[1].
Especially the rhythm and timing is often very jarring making words difficult to understand, especially when the pitch is not quite right.
It also doesn't seem to know about pacing, ignoring semicolon and comma.
Combined I often need to think hard about what it just said, or even listen to it again.
I also notice these issues in the various English voice models to varying degrees, so seems to be an inherent problem. Or can it be improved significantly with training it yourself?
[1]: https://rhasspy.github.io/piper-samples/
