With multilingual enabled in your room, your speakers will have to choose a language when they connect with their mic/webcam as below:
Once they have selected their language using the drop-down menu, they will still be able to change it in real time by clicking on the gear at the bottom right of their interface.
: Selection of the spoken language, which will also be the language in which the speaker will hear the interpreter.
: The speaker selects whether he wants to hear the interpreter translate the foreign language for him, or whether he only wants to hear the main audio of the room (so without the interpreter).