What this means for learners
Fe'efe'fe and Nupe share 33 sounds — roughly 75% of Nupe's inventory overlaps with Fe'efe'fe. 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 Nupe represent the greatest pronunciation challenge for Fe'efe'fe 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, Fe'efe'fe has 11 sounds not used in Nupe. Native Nupe speakers learning Fe'efe'fe 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.