Learn Croatian: Svi joj žele zahvaliti na važnom doprinosu i predanosti. - Everyone wants to thank her for the important contribution and dedication.

In English, we thank someone directly ("thank her"), but in Croatian, the verb zahvaliti (to thank) requires the Dative case for the person. You can think of it as giving thanks to someone. That is why we use the Dative enclitic joj.

Why does the sentence use na instead of za to say "for"?

While za is the usual translation for "for", certain social verbs like zahvaliti (to thank) or čestitati (to congratulate) have a fixed structure. When stating the reason for the thanks, you must use the preposition na followed by the Locative case.

What case are važnom doprinosu and predanosti in?

They are both in the Locative case because they follow the preposition na. The adjective važnom matches the masculine noun doprinosu (contribution) in the Locative.

Why does predanosti end in "-i"? Isn't it a feminine noun?

Yes, predanost (dedication) is a feminine noun, but it belongs to a special group of feminine nouns that end in a consonant rather than "-a". For these nouns, the Locative ending is -i, which is why it becomes predanosti here.