My mother in law (from China) n my husband had a huge fight and she left the house today morning and still have not return. She also switch off her phone. She is 70 and only speaks Mandarin. Husband heck care. I dont know what to do. Should I go to the police?

Lodge a missing person report at any police service counter. There is no minimum time required for the missing person to have lost contact with family members before the report can be lodged. After the report is lodged, you can post on your social media, have a picture of your MIL and ask your friends to share (and their friends will share). Some of my friends have done this after their elderly parents or grandparents wandered off and this method seems to work each time. You should also convince your husband to put aside his ego and follow you to all of your MIL's usual hang outs (where she usually meets her friends; maybe the market or the park).