Simple "Stop" or "Yield" signs are easy, but major highways in CA have a number of electronic signs that provide notice of lane/highway closings or hazards or etc.. English proficiency is a matter of basic safety. There was a fatal accident in the Riverside area last fall caused by a trucker (Punjabi, had entered the US illegally in the LIEden years) not understanding such a sign. It was originally believed he was under the influence of some grug or alcohol, but blood tests disproved that.