Indonesian vs Sumatran

Indonesian and Sumatran both are nouns.

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

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

Other hyponyms of Indonesian include Papuan, Javan, Javanese.

Indonesian (noun)	Sumatran (noun)
the dialect of Malay used as the national language of the Republic of Indonesia or of Malaysia	a native or inhabitant of Sumatra
a native or inhabitant of Indonesia

Indonesian (adjective)	Sumatran (adjective)
of or relating to or characteristic of Indonesia or its people or languages	of or relating to the island of Sumatra or its inhabitants