Only in Icelandic 27
What this means for learners
Icelandic and Yay share 18 sounds — roughly 40% of Yay's inventory overlaps with Icelandic. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 20 sounds found only in Yay represent the greatest pronunciation challenge for Icelandic 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, Icelandic has 27 sounds not used in Yay. Native Yay speakers learning Icelandic 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.