Hálsmenið hennar er fallegt, en hún finnur ekki eyrnalokkana sína.

Because -ið is the definite article attached to a neuter singular noun.

• hálsmen = necklace
• hálsmenið = the necklace

In Icelandic, the definite article is usually added to the end of the noun instead of being a separate word like English the.

Adjectives in Icelandic must agree with the noun in gender, number, and case.

Here the noun is hálsmenið, which is:

• neuter
• singular
• nominative (because it is the subject)

So the adjective has to take the matching form:

• fallegur = masculine
• falleg = feminine
• fallegt = neuter

That is why the sentence has Hálsmenið hennar er fallegt.

They are different forms of the same pronoun.

• hún = she → used as a subject
• hennar = her / hers → a genitive form, often used to show possession

So:

• hún finnur ekki... = she does not find...
• hálsmenið hennar = her necklace

English uses she / her; Icelandic does something similar, but with a fuller case system.

This is one of the most important Icelandic grammar points: ordinary possessive pronoun vs reflexive possessive.

In the first clause:

Hálsmenið hennar er fallegt

We use hennar because the possessor is not expressed as the subject of the clause in a way that calls for the reflexive. This is the normal way to say her necklace here.

In the second clause:

hún finnur ekki eyrnalokkana sína

We use sína because the possessor is the same person as the subject hún. So sína means her own.

A useful way to remember it:

• hennar = her
• sinn / sín / sitt = his/her/their own, referring back to the subject of the clause

Not usually.

• eyrnalokkana sína = her own earrings; the earrings belong to the subject hún
• eyrnalokkana hennar = usually her earrings, where her refers to some other female person, not the subject

So in this sentence, sína is the natural choice because the woman is looking for her own earrings.

Because sinn changes form to match the noun it goes with.

The noun eyrnalokkana comes from eyrnalokkur, which is:

• masculine
• plural
• accusative here

The matching accusative plural masculine form of sinn is sína.

So:

• eyrnalokkana sína = correct

If the noun were feminine plural, you would often get sínar instead.

Because it is the definite accusative plural form of eyrnalokkur.

Breakdown:

• eyrnalokkur = earring (singular)
• eyrnalokkar = earrings (nominative plural)
• eyrnalokka = earrings in the accusative plural
• eyrnalokkana = the earrings in the accusative plural

It is accusative because it is the direct object of finnur.

Finna normally takes a direct object in the accusative.

So in this sentence:

• hún finnur = she finds
• eyrnalokkana = the thing being found, so it is in the accusative

This is why you do not see the nominative plural eyrnalokkar here.

Because in a normal Icelandic main clause, the finite verb comes early, and ekki usually comes after that finite verb.

So:

• hún finnur ekki... = correct

This is the normal Icelandic word order for negation in a sentence like this.

English says:

• she does not find
• she can't find

Icelandic often expresses that with:

• subject + finite verb + ekki
  • object

Yes, very normal.

Icelandic often uses:

• the noun + definite article + possessive

So you get patterns like:

• bíllinn minn = my car
• bókin þín = your book
• hálsmenið hennar = her necklace

This can feel backwards to an English speaker, because English usually puts the possessive first, but in Icelandic this structure is extremely common.

Here are the key forms:

• hálsmenið → dictionary form hálsmen = necklace
• hennar → pronoun form related to hún
• er → dictionary form vera = to be
• fallegt → dictionary form fallegur = beautiful
• en = but
• hún = she
• finnur → dictionary form finna = to find
• ekki = not
• eyrnalokkana → dictionary form eyrnalokkur = earring
• sína → dictionary form sinn = reflexive possessive own

Looking up dictionary forms is especially important in Icelandic, because the words you see in a sentence are often inflected.

A rough English-friendly guide:

• Hálsmenið ≈ HOWLS-meh-nith
• hennar ≈ HEN-nar
• fallegt ≈ FAH-legt
• hún ≈ hoon
• finnur ≈ FIN-nur
• ekki ≈ EHK-ki
• eyrnalokkana ≈ AYR-na-lok-ka-na
• sína ≈ SEE-na

A few helpful pronunciation notes:

• á is usually like ow in cow
• ú is roughly like oo in food
• ð is like th in this
• stress is usually on the first syllable in Icelandic words

So the whole sentence has strong first-syllable stress throughout.