What this means for learners
Javanese and Lahu share 23 sounds — roughly 50% of Lahu's inventory overlaps with Javanese. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 23 sounds found only in Lahu represent the greatest pronunciation challenge for Javanese 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, Javanese has 10 sounds not used in Lahu. Native Lahu speakers learning Javanese 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.