What this means for learners
GUGU-YALANDYI and TETUN share 10 sounds — roughly 53% of TETUN's inventory overlaps with GUGU-YALANDYI. 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 TETUN represent the greatest pronunciation challenge for GUGU-YALANDYI 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, GUGU-YALANDYI has 6 sounds not used in TETUN. Native TETUN speakers learning GUGU-YALANDYI 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.