What this means for learners
BRUU and Madurese share 18 sounds — roughly 43% of Madurese's inventory overlaps with BRUU. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 17 sounds found only in Madurese represent the greatest pronunciation challenge for BRUU speakers. The adult brain tends to map unfamiliar sounds onto the closest native equivalent — a process that produces the characteristic "accent" of a second-language speaker. Learning to hear and produce these sounds as distinct requires focused ear training, not just repetition.
Conversely, BRUU has 24 sounds not used in Madurese. Native Madurese speakers learning BRUU will face the mirror-image challenge with these sounds.
Phoneme inventories from PHOIBLE. Data reflects one documented inventory per language; some variation exists across dialects and sources.