SpiderBasic

I had no idea there was TTS in native JS engines.. I assumed this would take a Cordova module..

Maybe some people not having it work has to do with CORS settings or localization?

It entirely depends what voices your OS has available. On Windows I think it uses SAPI, or OneCore. I hope not OneCore, because if they use that, that means it'll break on N editions of Windows.
All the official docs say are:

Again, most OSes have some kind of speech synthesis system,
which will be used by the API for this task as available.