What this means for learners
Chuvash and Javanese share 20 sounds — roughly 51% of Javanese's inventory overlaps with Chuvash. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 13 sounds found only in Javanese represent the greatest pronunciation challenge for Chuvash 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, Chuvash has 19 sounds not used in Javanese. Native Javanese speakers learning Chuvash 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.