Comment by Aachen
$ apt install espeak-ng
$ espeak-ng 'Hello, World!'
It takes some adjustment and sounds a lot worse than what e.g. Google ships proprietarily on your phone, but after ~30 seconds of listening (if I haven't used it recently) I understand it just as well as I understand the TTS engine on my phoneIf there's a more modern package that sounds more human that's a similar no-brainer to install, I'd be interested, but just to note that this part of the problem has been solved for many years now, even if the better-sounding models are usually not as openly licensed, orders of magnitude more resource-intensive, limited to a few languages, and often less reliable/predictable in their pronunciation of new or compound words (usually not all of these issues at once)