Við steikjum sveppi og hvítlauk í olíu áður en við bætum kjúklingnum við.

Because they are two different words:

• Við at the beginning means we
• við at the end is a particle that belongs to the verb bæta við, which means to add

So:

• Við steikjum ... = We fry ...
• við bætum kjúklingnum við = we add the chicken

This is very common in Icelandic: a verb plus a small particle can act like one meaning unit, a bit like English add in, take off, throw out.

Kjúklingnum means the chicken in the dative singular.

There are two things happening here:

1. The noun is kjúklingur = chicken
2. Icelandic usually adds the definite article the to the end of the noun instead of writing it as a separate word

Also, the verb expression bæta við requires the thing being added to be in the dative.

So:

• kjúklingur = chicken
• kjúklingi = to/for chicken, or chicken in the dative
• kjúklingnum = the chicken in the dative

So the ending -num reflects both case and definiteness.

Because bæta við governs the dative for the thing being added.

A useful pattern is:

• að bæta einhverju við = to add something

Here, einhverju is dative, so the actual noun also has to be dative:

• bæta kjúklingnum við = add the chicken

This is something Icelandic learners have to get used to: many verbs and verb-particle combinations require a specific case, and that case is not always the one English speakers would expect.

Because sveppi is the accusative plural of sveppur = mushroom.

The verb steikjum takes a direct object, so mushrooms appears in the accusative.

A quick pattern:

• sveppur = a mushroom
• sveppi = mushrooms, as a direct object

So in:

• Við steikjum sveppi ...
  We fry mushrooms ...

the form sveppi is exactly the form the sentence needs.

In Icelandic, hvítlaukur is often used as a singular noun meaning garlic, much like English uses garlic as a mass noun.

Here:

• hvítlauk = accusative singular of hvítlaukur

So sveppi og hvítlauk is literally:

• mushrooms and garlic

That is completely natural in a cooking sentence. If you wanted to be more specific about cloves, Icelandic often uses hvítlauksrif = garlic clove(s).

Because Icelandic has:

• no indefinite article like English a/an
• a suffixed definite article instead of a separate word for the

So:

• sveppi can mean mushrooms or some mushrooms
• hvítlauk can mean garlic
• olíu can mean oil

If Icelandic wants to say the mushrooms or the garlic, it usually adds the article to the noun:

• sveppina = the mushrooms
• hvítlaukinn = the garlic

Recipe language often uses bare nouns like this.

After the preposition í, Icelandic uses:

• accusative for motion into
• dative for location or state in

Here, í olíu means in oil as the cooking medium, so it is understood as dative.

One small complication: for olía, the form olíu looks the same in both accusative and dative singular. So the form itself does not show the difference, but the grammar behind it is still important.

Compare the general idea:

• í húsi = in a house
• í hús = into a house

In your sentence, the meaning is clearly the first type: in oil, not into oil.

Áður en is a fixed expression meaning before when it introduces a clause.

So:

• áður en við bætum kjúklingnum við
  = before we add the chicken

You can think of it as:

• áður = earlier / before
• en = introducing the following clause

Together they work like English before in sentences such as before we add the chicken.

Because Icelandic often prefers a full clause with its own subject and finite verb:

• áður en við bætum kjúklingnum við
• literally before we add the chicken

English is very happy to use before adding the chicken, but Icelandic often sounds more natural with the full clause. So repeating við here is completely normal.

Both are 1st person plural present verb forms, matching við = we.

• steikjum comes from steikja = to fry / sauté / cook in a pan
• bætum comes from bæta = to improve, add; with við, bæta við = to add

So:

• Við steikjum = we fry / we sauté
• við bætum ... við = we add ...

The verb endings show person and number, but Icelandic still normally keeps the subject pronoun too.

In cooking, steikja is a fairly broad word. Depending on context, it can mean:

• fry
• pan-fry
• sauté
• sometimes more generally cook in a pan

Because the sentence says í olíu, an English recipe might naturally translate it as fry or sauté depending on style. So if you saw slightly different English translations, that would be normal.

Because in Icelandic, with verb-particle combinations like bæta við, the object often comes between the verb and the particle:

• bætum kjúklingnum við

This is similar to how English can say:

• add the chicken in
• throw it out
• pick the book up

So the structure is very natural Icelandic word order for this kind of verb. The meaning is still one unit: bæta við = add.