I am also quite irritated by the fact that many TTS fail to state what language (and probably even dialect) they support. Actually to support a really good workflow for many Europeans (and probably also the rest of the world) one would actually need a multi language models that also support the use foreign words within one's own language. I am using a local notification reader on my smartphone (with SherpaTTS) and the mix of notification language as well as languages embedded in each other makes the experience rather funny at times.

Agreed.

I think they should have added the fact that it's English only in the title at the very least.

I echo this. For a TTS system to be in any way useful outside the tiny population of the world that speaks exclusively English, it must be multilingual and dynamically switch between languages pretty much per word.

Cool tech demo though!