German language vs High German

German language and High German both are nouns.

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

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

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

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

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