Breakdown of Við ætlum að syngja í þessari kirkju.
við
we
að
to (infinitive marker)
í
in / into / to (before the hour, in telling time) / per (in frequency expressions)
ætla
to intend
Questions & Answers about Við ætlum að syngja í þessari kirkju.
Why is 'this' translated as þessari here?
Þessari is the feminine dative singular form of þessi (this). We use it here because the preposition í requires the dative case when talking about a stationary location, and the word for church (kirkja) is a feminine noun.
Why did kirkja change to kirkju?
In Icelandic, words change their endings to match the grammatical case. Because the preposition í forces the dative case for a location, the feminine noun kirkja changes to its dative form, kirkju. The demonstrative pronoun þessari and the noun kirkju have to match in gender, number, and case!
We learned that ætla means 'to intend'. Why is it translated as 'going to' in this sentence?
While ætla literally means 'to intend' or 'to plan', it is the standard way to express future plans in Icelandic. Saying you intend to do something naturally translates to 'going to' do it. It is always followed by að plus the infinitive verb, which here is að syngja (to sing).
Does the preposition í always make the words after it dative?
Not always! The preposition í takes the dative case when it describes a stationary location, meaning where an action is currently happening. If there were movement from one place into another, like walking into the church, í would trigger the accusative case instead.