What this means for learners
Iai and Javanese share 28 sounds — roughly 54% of Javanese's inventory overlaps with Iai. 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 Javanese represent the greatest pronunciation challenge for Iai 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, Iai has 24 sounds not used in Javanese. Native Javanese speakers learning Iai 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.