The lang property of the SpeechRecognition interface returns and sets the language of the current SpeechRecognition. If not specified, this defaults to the HTML lang attribute value, or the user agent's language setting if that isn't set either.

API Experimental lang Property recognition Reference speech SpeechRecognition Web Speech API

The lang property of the SpeechSynthesisUtterance interface gets and sets the language of the utterance.

API Experimental lang Property Reference speech SpeechSynthesisUtterance synthesis Web Speech API

The lang read-only property of the SpeechSynthesisVoice interface returns a BCP 47 language tag indicating the language of the voice.

API Experimental lang Property Reference speech SpeechSynthesisVoice synthesis Web Speech API