What this means for learners
Tagalog and Indonesian share 19 sounds — roughly 61% of Indonesian's inventory overlaps with Tagalog. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 12 sounds found only in Indonesian represent the greatest pronunciation challenge for Tagalog 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, Tagalog has 9 sounds not used in Indonesian. Native Indonesian speakers learning Tagalog 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.