What should I do? I have been abroad in Japan, and I am too tired to work since I came here. What if Japanese is not good?

This is the working atmosphere in Japan. Learn to accept difficulties, think about the original rhetoric, come on. By the way, I recommend you to watch the documentary Youth on the Other Side, which is also about the hard life of Japanese who work and study in China. Everyone has a hard time at first, and I hope it will bring you courage. Japanese is not good, which means you can still learn some. Go on learning. In that environment, if you study now, it will be more difficult at first, and the more you learn, the more confident you will be. This is the state of Japanese work, diligence, stubbornness and fortitude. Learning more from them may be a reconstruction of your life. It's hard to stay at home, but come on when you go out.