The Google TTS API support a mere 33 languages yet mess up its results. Its free and that's the only thing it has going for itself as a lot of times it messes up the accents/pitches and pauses.
I started using an external text to speech AI for this reason. This supports more languages and thankfully I have 250+ natural-sounding voices to choose from when I render the audio
Can you please show us how to use that in App Inventor
Taifun
PS: thread unlisted meanwhile