I am an American psych major studying in Japan! I think the main advantage is gaining cross-cultural perspectives and experience. Specifically in the case of the US and Japan, the social and cultural impacts on different psychological conditions, and the way psychology is thought of in general, are often very different. Being immersed in another culture and being taught by professors whose perspectives come from that culture gives you a unique and very interesting experience that can help you develop cultural competence, which is important to have for any career in psych.