Is there a performance disparity between men and women in a patriarchal institution? We investigate this question concerning the current debate on gender stereotypes and egalitarianism. Informed by a recent study of the vocal data of the US Supreme Court justices, we apply a machine-learning algorithm to an original audio dataset of 1,400 criminal trials in Chinese courtrooms, identifying cues indicating the Standard Mandarin (\textit{Putonghua}) proficiency of judges. We found that men and women judges, despite working in a patriarchal institution, are equally competent in oral Standard Mandarin.