Japanese Language/Diglossia

Diglossia is a linguistic phenomenon where two different languages or varieties of a language are used within society under different functional conditions. According to Ferguson (1959),  H(igh) represents the high variety and L(ow) represents low variety. H has a formal function and L has a more casual function.

Keigo (Honorifics)
In Reischauer and Jansens (1995)’s article, Japanese society has hierarchical differences because of its recent feudal history marked with different ranks and statuses. These differences influence the use of Japanese in terms of interpersonal relations. Japanese language has honorifics which consist of two forms: the respect form and humble form. For example, the Japanese need to use honorifics when they talk to a social superior. They show respect by humbling themselves and socially raising their partner. In this sense, the use of honorifics is considered H. In contrast, when the Japanese converse to someone at the same social level, such as a co-worker or friend, they use more casual language L.

Hougen (Dialects)
Furthermore, Japan consists of various regions where dialects differ, so in order to survive in that particular region, it is important that one understand the dialect L that is used in that area. However, since these regions are a part of Japan, those who live in those dialectical regions also need to understand standard Japanese H, which is used in formal situations such as politics, the media, business, and education.

Reference:

 * Reischauer, E.O., & Jansen, M.B. (1995). The Japanese today: change and continuity. Cambridge, MA: The Belknap Press of Harvard University Press.
 * Garcia, . (2009). Bilingual education in the 21st century. West Sussex,U.K.: Wiley-Blackwell.