真金不怕火炼 True gold does not fear the fire. Said of what is right, and of upright people, who stand any test.
事实胜于雄辩 Facts are stronger than eloquence.
半瓶醋 Half a bottle of vinegar. A person with a little knowledge or skill, but not much. A dictionary example: “Listen to him talk big. In fact, he is only half a bottle of vinegar.”
班门弄斧 To swing an axe at the door of Lu Ban, the master carpenter. To show off one’s skill in front of experts.
真人不露相，露相不真人 The true master does not show his face. The one who shows his face is not a true master. Said of people with real ability who do not make a show of it. (Journey to the West)
大智若愚 Great wisdom seems foolish. Said of people of outstanding talent who do not show it.