Ég hlusta á hljóðbók í strætó, jafnvel þegar ég er þreyttur.

Because hlusta is one of those Icelandic verbs that normally takes the preposition á with the thing you are listening to.

So Icelandic says:

hlusta á tónlist = listen to music
hlusta á hljóðbók = listen to an audiobook

This is something you largely have to learn with the verb. The á here is not the ordinary location word on; it is just the preposition that belongs with hlusta.

It is in the accusative, because hlusta á takes an accusative object.

So in Ég hlusta á hljóðbók, the noun after á is accusative.

A useful detail: hljóðbók is a feminine noun, and in the singular its nominative and accusative forms are the same, so you do not see any visible change here. That is why it still looks just like the dictionary form.

Icelandic does not have a separate indefinite article like English a/an.

So:

hljóðbók can mean an audiobook or audiobook, depending on context.

If you wanted the audiobook, Icelandic would usually add the definite article to the end of the noun:

hljóðbókin = the audiobook

So the sentence uses the plain indefinite form: hljóðbók.

This is just an idiomatic difference between the languages.

English usually says on the bus, but Icelandic usually says í strætó, literally in the bus. Icelandic often treats being in a vehicle as being physically inside it.

So:

í strætó = on the bus
í bílnum = in the car
í lestinni = on the train / in the train

Also, with í, Icelandic distinguishes between:

• movement into something: often accusative
• location inside something: often dative

Here the meaning is location, so í is behaving like in/inside. The noun strætó just happens to look the same in this form.

In everyday Icelandic, strætó usually means a bus, especially a city bus or public bus.

Depending on context, it can also refer more broadly to the bus system. But in a sentence like this, í strætó is naturally understood as on the bus.

It is a very common everyday word, and learners will hear it a lot.

Jafnvel means even.

Here it emphasizes the following time clause:

jafnvel þegar ég er þreyttur = even when I am tired

So it adds the idea that this is true in a slightly surprising situation too. The speaker listens to audiobooks on the bus, and this remains true even when they are tired.

Because þegar introduces a subordinate clause, and subordinate clauses normally do not use the main-clause verb-second pattern.

So the normal order is:

þegar + subject + verb

That gives:

þegar ég er þreyttur

Compare:

• Main clause: Ég er þreyttur.
• Subordinate clause: þegar ég er þreyttur

For English speakers, this often feels quite natural, because English also keeps normal subject-verb order after when.

Because Icelandic often uses commas before subordinate clauses more regularly than English does.

Here, þegar ég er þreyttur is a subordinate clause introduced by þegar, and the comma helps mark that boundary:

Ég hlusta á hljóðbók í strætó, jafnvel þegar ég er þreyttur.

In English, a comma here might be more optional depending on style. In Icelandic, this comma is very normal.

Yes. Þreyttur is an adjective, and it agrees with the subject in gender, number, and case.

Here it matches ég referring to a masculine singular speaker, so you get:

ég er þreyttur = I am tired

If the speaker were feminine, you would usually say:

ég er þreytt

So this sentence suggests that the speaker is male, unless it is just being used as a dictionary-style example.

It can mean either, depending on context.

The Icelandic present tense often covers both:

• I listen
• I am listening

In this particular sentence, the meaning is probably habitual: the speaker generally listens to audiobooks on the bus, even when tired.

So the most natural interpretation is something like I listen to audiobooks on the bus, even when I’m tired, rather than describing only one single moment.