Woah, someone is learning Bulgarian. I live in Bulgaria. 
We’re doing a big upgrade soon on the catalogues, I think I’ll be able to make proper TurtleTube playlists, and, integrate this course into LR: The Yojik Website
Ok so text mode uses the browsers built-in TTS function for audio. You can see what languages/voices your browser supports here: Web Speech Synthesis Demo (codepen.io) fyi, MS edge has nicer voices than Chrome.
@Miths do you see Bulgarian in the list on the test page?
Text mode is pretty neglected, should handle the case of missing TTS language.