Learn Icelandic: Viltu ostabakkann, þá er ég til í að deila honum. - Should you want the cheese platter, then I am up for sharing it.

Vera til í is an idiom meaning "to be up for" or "to be willing to." Because the thing you are willing to do here is an action, it is followed by að plus the infinitive verb deila (to share). If you were just up for a noun, like "a coffee", you would use the accusative case instead: ég er til í kaffi.

Why does the sentence start with the verb viltu (do you want) instead of using the word ef (if)?

Starting a sentence with a verb is a very common way in Icelandic to express a condition without actually using the word ef. It translates neatly to "Should you want..." or "If you want...". The word þá (then) in the second clause naturally completes this "if-then" structure.

Why is the pronoun at the end honum (dative) when it refers back to ostabakkann (accusative)?

A pronoun must take the case required by the verb it directly pairs with in its own clause, not the case the noun had earlier. While ostabakkann is in the accusative case because it is the object of vilja (to want), the verb deila (to share) strictly dictates a dative object. Therefore, the masculine pronoun hann must shift to the dative honum.

How exactly is the compound word ostabakkann put together?