Indonesian vs Sundanese

Indonesian and Sundanese both are nouns.

Word	Noun	Adjective	Verb	Adverb
Indonesian	Yes	Yes	No	No
Sundanese	Yes	No	No	No

As nouns, Sundanese is a hyponym of Indonesian; that is, Sundanese is a word with a more specific, narrower meaning than Indonesian:

Indonesian: the dialect of Malay used as the national language of the Republic of Indonesia or of Malaysia
Sundanese: the Indonesian language spoken on West Java

Other hyponyms of Indonesian include Javanese, Javanese language, Sundanese language, Balinese, Balinese language.

Indonesian (noun)	Sundanese (noun)
the dialect of Malay used as the national language of the Republic of Indonesia or of Malaysia	the Indonesian language spoken on West Java
a native or inhabitant of Indonesia

Indonesian (adjective)	Sundanese (adjective)
of or relating to or characteristic of Indonesia or its people or languages