Learn Icelandic: Þau giftust í fallegri kirkju. - They got married in a beautiful church.

In Icelandic, the neuter plural pronoun þau is used whenever you refer to a mixed-gender group. If this sentence were about a same-sex couple, you would use the masculine þeir or the feminine þær instead.

Why does the verb giftust end in -st?

This is the middle voice form of the verb gifta. The active verb gifta means to marry someone off or to perform a marriage ceremony. Adding the -st ending creates the verb giftast, which carries a reciprocal meaning: to get married to each other.

Why are fallegri and kirkju in the dative case?

The preposition í governs the dative case when it indicates a static location, answering the question 'where?'. Since the couple got married inside the church, the feminine noun kirkja changes to its dative form kirkju, and the adjective describing it must match this case.

Where does the -ri ending on fallegri come from?

Because the noun is indefinite (a beautiful church, not THE beautiful church), the adjective takes the strong declension. For a feminine dative singular adjective, the strong ending is -ri, changing the base word fallegur to fallegri.