Japanese vs Japanese language

Japanese and Japanese language both are nouns.

Word	Noun	Adjective	Verb	Adverb
Japanese	Yes	Yes	No	No
Japanese language	Yes	No	No	No

As nouns, Japanese and Japanese language are synonyms defined as:

Japanese and Japanese language: the language (usually considered to be Altaic) spoken by the Japanese

Japanese (noun)	Japanese language (noun)
the language (usually considered to be Altaic) spoken by the Japanese	the language (usually considered to be Altaic) spoken by the Japanese
a native or inhabitant of Japan

Japanese (adjective)	Japanese language (adjective)
of or relating to or characteristic of Japan or its people or their culture or language