This study was interested in group differences in Indonesia in bilingualism, whether vocabulary knowledge shows a differential pattern across the languages, and whether language skill and usage differences between groups are moderated by contextual factors, such as ethnic group size. It explored bilingualism among non-immigrant adolescents in an under-researched, non-WEIRD (western, educated, industrialized, rich, democratic) society. The study shows the role of language usage and skill that is different from a western context in various aspects, such as the dominance of L2 in all groups.