What this means for learners
NDUT and TETUN share 16 sounds — roughly 47% of TETUN's inventory overlaps with NDUT. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 3 sounds found only in TETUN represent the greatest pronunciation challenge for NDUT 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, NDUT has 18 sounds not used in TETUN. Native TETUN speakers learning NDUT 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.