I don't understand your question. What do you mean by defending themselves? Physically or legally? If someone is resisting arrest, law enforcement will be working towards compliance. If they are cuffed and compliant, it is typically very clear if the person detained is mute, deaf, non-English speaking, or so fucked-up on drugs that communication is impossible. If someone is mute/deaf, I've seen notepads used for communication. If non-English speaking, I've seen/ used Google Translate (not the best but better than nothing) if a translator isn't available. Once before a magistrate, the judiciary has a call-in service for translators. If someone is high they'll be evaluated medically and either taken to a hospital for care or to a jail to sober up if medical intervention isn't needed.