depending on the source the number of foreigners imprisoned in China over the last ten years seems to be about a few dozen to 200. About two million Europeans travel to China per year so very low. I'm German and have spent several months at a time in China over the last ten years. If you're just a random guy it's completely fine. Contrary to the other reply, posting on social media or teaching English doesn't land you in prison, and China isn't like Nazi Germany.