Við komum þaðan seint í gærkvöldi.

Yes:

• Við = we
• komum = came here, from the verb koma = to come
• þaðan = from there
• seint = late
• í gærkvöldi = last night / yesterday evening

A very literal order would be:

We came from there late yesterday evening.

Because komum can be either present or past depending on context.

• við komum can mean we come
• við komum can also mean we came

In this sentence, í gærkvöldi means last night / yesterday evening, so the time expression makes it clearly past.

So:

• Við komum á hverjum degi = We come every day
• Við komum í gærkvöldi = We came last night

The infinitive is koma, meaning to come.

This verb is very common, and its forms are not all built in a perfectly predictable way, so it is worth learning as a full verb:

• að koma = to come
• ég kem = I come
• við komum = we come
• ég kom = I came
• við komum = we came

So komum is the 1st person plural form: we come / we came.

Þaðan means from there.

By contrast:

• þar = there
• þangað = to there / there, toward that place
• þaðan = from there

This is a very useful Icelandic pattern: place words often distinguish:

• location
• motion toward
• motion away from

So in this sentence, þaðan specifically shows movement away from a place.

Because þaðan already includes the idea of from.

English uses two words:

• from there

Icelandic often uses just one:

• þaðan

So Við komum þaðan already means We came from there. You do not need frá here.

Because seint is an adverb, not an adjective.

It describes how/when the action happened:

• We came late

It does not describe we, so it does not agree with the subject.

A useful thing to notice is that many Icelandic adverbs look like the neuter singular form of an adjective. Here:

• adjective: seinn = late
• adverb: seint = late

So:

• seinn maður = a late man or a man who is late
• við komum seint = we came late

It means last night or yesterday evening, depending on context.

More literally:

• í = in
• gærkvöldi = yesterday evening in a declined form

As a whole, í gærkvöldi is a normal Icelandic time expression meaning something like:

• yesterday evening
• last night

In everyday English, last night is often the most natural translation.

Because it is in the dative after the preposition í in this time expression.

The preposition í can take different cases depending on meaning. With time expressions like this, it commonly takes the dative.

So the noun appears in a dative form:

• basic form: gærkvöld
• here: gærkvöldi

You do not need to overthink it at first; it is very helpful simply to learn í gærkvöldi as a fixed expression meaning last night / yesterday evening.

The given word order is natural, but Icelandic word order is fairly flexible.

This sentence is:

• Við = subject
• komum = finite verb
• þaðan = place/direction
• seint í gærkvöldi = time

You can move parts of the sentence for emphasis, but Icelandic usually keeps the finite verb in second position in main clauses.

For example:

• Í gærkvöldi komum við þaðan seint.

That is still grammatical, but once Í gærkvöldi is placed first, komum must come next, before við.

So the original sentence is a straightforward, neutral way to say it.

Not quite.

• í gær = yesterday
• í gærkvöldi = yesterday evening / last night

So í gærkvöldi is more specific. It tells you the action happened in the evening or night, not just sometime yesterday.

Not usually as the main translation.

The verb koma basically means come, and with þaðan it means come from there.

So the most direct sense is:

• We came from there late last night

In some contexts, English may use arrived more naturally, but that depends on what the speaker is focusing on. Grammatically, the Icelandic sentence is built around coming from a place, not specifically arriving at a destination.