any xx-XX language code
You can check for additional language codes here.
The transcription service uses default browser / system mic as a source and cannot be muted. Generally needs to be used in conjunction with &cc
You will normally need Internet access for this to work and be willing to tolerate the occasional hiccup that the browser's transcription service may cause. Service may stop for seconds at a time as a result. Certain Android devices may not require internet for the transcription to work.