What this means for learners
Nez Perce and Squamish share 16 sounds — roughly 43% of Squamish's inventory overlaps with Nez Perce. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 21 sounds found only in Squamish represent the greatest pronunciation challenge for Nez Perce 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, Nez Perce has 20 sounds not used in Squamish. Native Squamish speakers learning Nez Perce 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.