High German vs German language

High German and German language both are nouns.

Word	Noun	Adjective	Verb	Adverb
High German	Yes	No	No	No
German language	Yes	No	No	No

As nouns, High German and German language are synonyms defined as:

High German and German language: the standard German language; developed historically from West Germanic

Other synonyms of High German include German, High German language.

High German (noun)	German language (noun)
the standard German language; developed historically from West Germanic	the standard German language; developed historically from West Germanic