Guoyu vs Mandarin Chinese

Guoyu

name
  • The standardized spoken Chinese language, also referred to as Standard Mandarin. The term remains in common use in the Republic of China (Taiwan) and colloquially in Hong Kong (along with Putonghua). In mainland China, Guoyu or Taiwan Guoyu is used to refer to Taiwanese Mandarin (standard), as opposed to mainland standard Mandarin. 

  • The language the Emperor of China spoke. 

Mandarin Chinese

noun
  • Standard Mandarin. 

  • A group of related Chinese dialects spoken across most of northern and southwestern China. 

How often have the words Guoyu and Mandarin Chinese occurred in a corpus of books? (source: Google Ngram Viewer )