German language vs High German language

German language and High German language both are nouns.

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

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

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

Other synonyms of German language include German, High German.

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