Learn Icelandic: Lögreglan bíður í stóra réttarsalnum.

Because the noun réttarsalnum (the courtroom) has the definite article suffix, the adjective must use the weak declension. In the weak declension, all masculine adjectives in the oblique cases (accusative, dative, and genitive) end in -a. Since the preposition í requires the dative case here, we use stóra.

Why is the verb bíður (waits) singular when the English translation says wait (plural)?

In English, the word police is treated as a plural noun. In Icelandic, however, lögreglan is a singular feminine noun (think of it as the police force). Because it is a singular noun, it takes the 3rd person singular form of the verb, which is bíður.

Why are we using the dative case for réttarsalnum instead of the accusative?

The preposition í (in) can take either the accusative or the dative case. We use the accusative when describing movement to a destination, but we use the dative when describing a stationary location. Since the police are just waiting inside the room, we use the dative case.

How is the compound word réttarsalnum put together?