[Feature request] Suggest SherpaTTS as an opensource offline TTS alternative

[lrq3000]

Thank you for wanting to share an idea! But before starting, ensure to check if this feature request respects the following requirements:

• It is written in English (I can translate what you say, but issues written in English are easier to read for the other users).
• There is not already a similar feature request among the open or closed issues.

Is your feature request related to a problem? Please describe.
This is a follow-up of #93 . Since then, a new breed of opensource TTS models were released and an opensource Android app, SherpaTTS, is now available and working well enough that I think it can safely be suggested as a companion to RTranslator, to offer a fully opensource and offline experience.

Each voice pack is about 60-120MB.

The app is here:

https://github.com/woheller69/ttsengine

(It is also on fdroid)

And it uses the voice packs and onnx from here (the engine is also available on desktop such as Windows, they offer executables):

https://github.com/k2-fsa/sherpa-onnx/releases/

Describe the solution you'd like
At app startup or in readme, SherpaTTS could be suggested as an alternative to have fully offline translation and TTS experience. This allows the Talkie Walkie mode to work fully offline for a lot of languages.

Describe alternatives you've considered
Compared to ESpeak, SherpaTTS offers high quality natural sounding voices (for the voices in medium or hign quality, there are also low quality voices packs which had a smaller dataset or worse recording conditions such as a non pro grade audio setup). Compared to RHVoice, SherpaTTS has voices of similar quality, but offers many more voices, all major languages are included, although not as many as NLLB supports.

Additional context
Ensure to change the TTS engine to SherpaTTS in Android settings. And download voice packs in SherpaTTS before trying to use them in RTranslator.