Shared sounds 37
What this means for learners
Maithili and Nepali share 37 sounds — roughly 50% of Nepali's inventory overlaps with Maithili. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 37 sounds found only in Nepali represent the greatest pronunciation challenge for Maithili 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, Maithili has 14 sounds not used in Nepali. Native Nepali speakers learning Maithili 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.