Ég heng sundfötin upp á svalirnar til að þorna.

It comes from the infinitive að hengja, meaning to hang or to hang up something.

Ég heng is the 1st person singular present tense: I hang. In this verb, the ég form is heng, not hengja. So:

• að hengja = to hang something
• ég heng = I hang

This is a very common question.

• að hengja = to hang something up; it is transitive, so it takes an object
• að hanga = to hang; it is intransitive, so the thing is already hanging

So:

• Ég heng sundfötin upp = I hang the swimwear up
• Sundfötin hanga á svölunum = The swimwear is hanging on the balcony

Because sundföt is normally a plural noun in Icelandic. It literally means something like swimming clothes.

So even when English might say a swimsuit or swimwear, Icelandic often uses sundföt in the plural.

The ending -in is the definite article attached to the noun, so:

• sundföt = swimwear / swimsuit
• sundfötin = the swimwear / the swimsuit

Here sundfötin is the direct object of heng, so it is in the accusative.

However, sundföt is a neuter plural noun, and in Icelandic the nominative and accusative are often the same in the neuter plural. So even though it is accusative here, the form still looks like sundfötin.

Upp is a particle meaning up. Together with hengja, it gives the idea of hanging something up, not just hanging in a vague sense.

So heng sundfötin upp is very close to English hang the swimwear up.

Because Icelandic often places this kind of particle after the object.

So heng sundfötin upp is a very natural word order. English can do something similar:

• hang the clothes up

That is why the sentence is not built as a word-for-word version of I hang up the swimwear.

Because á is the normal preposition used with svalir.

In Icelandic, you go out onto the balcony with á, not í. So:

• á svalirnar = onto the balcony
• á svölunum = on the balcony

This is just the idiomatic Icelandic way to talk about balconies.

Because svalir is a noun that is grammatically plural in Icelandic, even when it refers to what English calls a balcony.

So:

• svalir = balcony / balconies, depending on context
• svalirnar = the balcony / the balconies

This is a vocabulary point you mostly just have to learn as part of the word.

Because after á, Icelandic uses:

• accusative for movement toward a place
• dative for location in a place

In this sentence, the swimwear is being moved onto the balcony, so Icelandic uses the accusative:

• á svalirnar = onto the balcony

If the clothes were already there, you would use the dative:

• á svölunum = on the balcony

Til að introduces purpose. It means in order to, so as to, or so that.

So:

• til að þorna = in order to dry / so they can dry

It explains why the speaker is hanging the swimwear up.

Because þorna means to dry in the sense to become dry, while þurrka usually means to dry something or to wipe something dry.

So here the swimwear is being hung up so that it can become dry by itself:

• þorna = dry, become dry
• þurrka = dry something, wipe dry

That makes til að þorna the natural choice.

Normally you should say ég.

Even though Icelandic verbs do change for person and number, modern Icelandic usually keeps the subject pronoun in ordinary statements. So:

• Ég heng sundfötin upp... = the normal full sentence

Leaving out ég would usually sound incomplete outside special contexts such as poetry, diaries, or very informal note-like language.