That actually sounds like a fun game for multilingual people. Partner A picks language A, Partner B picks language B. Now, have a conversation with each other

That actually sounds like a fun game for multilingual people. Partner A picks language A, Partner B picks language B. Now, have a conversation with each other where you only speak in your chosen language. The listener must listen and translate in their head and then respond in their chosen language. First person to slip up and change languages loses.