diglossia
noun [ U ] language specialized uk/ˌdaɪˈɡlɒs.i.ə/ us/ˌdaɪˈɡlɑː.si.ə/
双层语言，双言现象（指在特定语言小区里，一种语言存在两种不同变体，各具特定的社会功能）
a situation in which there are two different forms of the same language used by a community, used in different social situations