What this means for learners
Dioula and Yao share 23 sounds — roughly 47% of Yao's inventory overlaps with Dioula. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 26 sounds found only in Yao represent the greatest pronunciation challenge for Dioula 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, Dioula has 16 sounds not used in Yao. Native Yao speakers learning Dioula 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.