TTS (text to speech) is not the same as STT (speech to text, aka voice recognition). and, of course, language translation is completely different. not clear what you are looking for.
the vosk library is speech to text, not text to speech.
the vosk library does not offer thai language support (at this time).
the website you show has nothing to do with vosk speech to text. it is a completely different project.
android has very good support both for TTS and STT. and i believe both support thai. offline supported.
both are not difficult to implement in b4a. you really do not want "continuous". there are many side effects.