What this means for learners
Chamorro and Makassar share 18 sounds — roughly 50% of Makassar's inventory overlaps with Chamorro. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 5 sounds found only in Makassar represent the greatest pronunciation challenge for Chamorro 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, Chamorro has 18 sounds not used in Makassar. Native Makassar speakers learning Chamorro 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.