What this means for learners
Ocaina and Japanese share 21 sounds — roughly 53% of Japanese's inventory overlaps with Ocaina. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 19 sounds found only in Japanese represent the greatest pronunciation challenge for Ocaina 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, Ocaina has 17 sounds not used in Japanese. Native Japanese speakers learning Ocaina 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.