What @eukgoekoko mentioned isn't a bad strategy. Ask them to introduce an English only policy. If the common language is English and there was no requirements

What @eukgoekoko mentioned isn't a bad strategy. Ask them to introduce an English only policy. If the common language is English and there was no requirements to speak Mandarin, then get the managers to change that. Otherwise quit and don't work at a Chinese sweatshop. No point working there if you can't understand anyone. I reckon, if that keeps going on, some tasks and requirements you were needed to do would be lost in translation. Then you're on the hook for that. People WILL always use the language their most comfortable in.