Hemlaljósið virkar.

Because Icelandic usually puts the definite article on the end of the noun instead of using a separate word like the.

So:

• hemlaljós = brake light / a brake light
• hemlaljósið = the brake light

The ending -ið is the definite article here, and it also shows that the noun is neuter singular.

It is singular: the brake light.

A tricky thing is that the basic form hemlaljós can look the same in singular and plural, because ljós is one of those neuter nouns whose indefinite singular and indefinite plural are identical in form.

Useful forms:

• hemlaljós = a brake light / brake lights depending on context
• hemlaljósið = the brake light
• hemlaljósin = the brake lights

So in your sentence, the ending -ið makes it clearly singular and definite.

Because Icelandic normally attaches the to the noun as a suffix.

English:

• the brake light

Icelandic:

• hemlaljósið

This is very common in Icelandic. For example:

• bíll = car
• bíllinn = the car

So hemlaljósið already includes the idea of the.

Virkar is a verb, from the infinitive virka.

In this sentence it is present tense, 3rd person singular.

That matches the subject hemlaljósið, which is treated as it in English:

• hemlaljósið = it / the brake light
• virkar = works / is working

So the structure is basically:

• The brake light works

Because virka is the infinitive form, like English to work.

In a full sentence with a subject, you need a finite verb form. Here that form is virkar, which is used with he/she/it in the present tense.

Compare:

• að virka = to work
• ég virka = I work
• þú virkar = you work
• það virkar = it works

Since hemlaljósið is a singular thing, the sentence uses the it works form: virkar.

Yes. Virka is very commonly used for something functioning properly.

So Hemlaljósið virkar means that the brake light is functioning.

This is very natural Icelandic for machines, systems, electronics, lights, and so on. It is much like English works in sentences such as:

• The phone works
• The internet works
• The light works

You usually add ekki after the verb:

• Hemlaljósið virkar ekki. = The brake light does not work.

That is the most direct negative version.

You may also hear something like:

• Hemlaljósið er bilað. = The brake light is broken.

But if you just want to negate the original sentence, virkar ekki is the straightforward pattern.

A rough learner-friendly pronunciation would be:

HEM-la-LYOH-sith VIR-kar

A few notes:

• ó is a long vowel, roughly like oh but not exactly English oh
• lj is often pronounced something like ly
• ð is the soft th sound, as in this
• stress in Icelandic usually falls on the first syllable of each word

So the main stress is on:

• HEM-laljósið
• VIR-kar

Only because it is the first word of the sentence.

Icelandic does not capitalize nouns the way German does. So in the middle of a sentence, it would normally be:

• hemlaljósið

not capitalized unless there is some special reason.

Yes. Icelandic makes a lot of compound nouns, and this is one of them.

It is built from:

• hemla- = related to brakes
• ljós = light

So the whole compound means brake light.

Compound words are extremely common in Icelandic, and learning to notice their parts can help a lot with vocabulary.

This sentence uses the basic Icelandic statement pattern:

• Subject + Verb

So:

• Hemlaljósið = subject
• virkar = verb

That gives:

• Hemlaljósið virkar.

If you wanted to turn it into a yes/no question, Icelandic often puts the verb first:

• Virkar hemlaljósið? = Does the brake light work?

So the statement and question can be distinguished partly by word order.

You would remove the definite ending:

• Hemlaljós virkar.

That gives an indefinite meaning such as a brake light works or brake light works, depending on context.

In practice, though, Icelandic often leaves indefiniteness less explicit than English does, so the exact best translation may depend on the situation. The important grammar point is:

• hemlaljós = indefinite
• hemlaljósið = definite