1, both economics and humanities and society need some mathematics and statistics.
2. official website of Kyushu University in Japan is in Chinese, including Japanese. Please read it carefully.
I suggest you contact the language school first. When you arrive in Fukuoka, you can contact professors from these nine universities directly from China. However, professors can't meet in person, interviews can't be conducted, and you can't see the basic state of your economy or knowledge. Many people refuse or don't answer you.