What this means for learners
AHTNA and Adzera share 16 sounds — roughly 46% of Adzera's inventory overlaps with AHTNA. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 9 sounds found only in Adzera represent the greatest pronunciation challenge for AHTNA 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, AHTNA has 19 sounds not used in Adzera. Native Adzera speakers learning AHTNA 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.