It is commonly believed that Japan is a homogeneous country. I somewhat agree that the cultural diversity level is low in Japan, in terms of language, geography and way of manner of thinking.
First, Japanese is the only language spoken on a daily basis. Even unskilled jobs require basic Japanese skills which is quite a high standard for non-native people.
Second, Japan is an island country. Divided by the seas from other countries, interacions with other ethnic groups have been rather limited historically. In addition, people in Japan have traditionally grown and accepted the sense of distinction between outside and inside. For example, foreigner is literally called "outsider" in Japanese.
Third, people in Japan share the value system, enbodied by harmony. One of the oldest laws in Japan stipulated the respect for harmony in the seventh century. To this day, people have been respecting others and caring about how they are seen by others, which leads to the deciplined, polite community.
However, there are several facts that should not be overlooked. Minorities, such as Chinese, Korean, Brazilian and Ainu, do exist. Moreover, shrinking working population is inviting more immigrants to Japan. Focusing on the language, Japanese is made of three types of letters, hiragana, kanji and katakana, which are, roughly speaking, used to describe something deriving from Japanese, Chinese and Western languages, respectively. In other words, Japanese is a classic example of cultural assimilation in Japan.
In conclusion, while it has several aspects to be considered diverse, Japan deserves being viewed as a homogeneous society.
