What this means for learners
Tongan; Tonga and Lahu share 11 sounds — roughly 24% of Lahu's inventory overlaps with Tongan; Tonga. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 35 sounds found only in Lahu represent the greatest pronunciation challenge for Tongan; Tonga 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, Tongan; Tonga has 6 sounds not used in Lahu. Native Lahu speakers learning Tongan; Tonga 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.