What this means for learners
Aché and Washkuk share 21 sounds — roughly 62% of Washkuk's inventory overlaps with Aché. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 10 sounds found only in Washkuk represent the greatest pronunciation challenge for Aché 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, Aché has 13 sounds not used in Washkuk. Native Washkuk speakers learning Aché 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.