What this means for learners
Russian and Croatian share 21 sounds — roughly 50% of Croatian's inventory overlaps with Russian. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 15 sounds found only in Croatian represent the greatest pronunciation challenge for Russian 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, Russian has 21 sounds not used in Croatian. Native Croatian speakers learning Russian 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.