What this means for learners
MBUM and Swahili share 25 sounds — roughly 66% of Swahili's inventory overlaps with MBUM. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 12 sounds found only in Swahili represent the greatest pronunciation challenge for MBUM 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, MBUM has 13 sounds not used in Swahili. Native Swahili speakers learning MBUM 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.