Skeggið hans er orðið of langt, svo hann rakar sig áður en gestirnir koma.

In Icelandic, possessors like hans often come after the noun, especially in ordinary, neutral statements.

So:

• skeggið hans = his beard

This is the most natural pattern here.
The version hans skegg is possible, but it usually sounds more marked, contrastive, or literary, something like his beard as opposed to someone else’s.

With body parts, Icelandic very often uses:

• definite noun + possessor
• so skeggið hans, hendurnar hennar, húsið þeirra, etc.

The -ið is the suffixed definite article, meaning the.

The base noun is:

• skegg = beard

With the definite article:

• skeggið = the beard

Icelandic usually adds the to the end of the noun instead of using a separate word like English does.

So:

• skegg = beard
• skeggið = the beard

In this sentence, Icelandic uses the definite form because it is talking about a specific beard: his beard.

Er orðið is a very common Icelandic way to express has become or has gotten.

Here:

• er = is
• orðið = become / become-state participle of verða

Together, er orðið often means:

• has become
• has gotten
• or more literally, is become

In natural English, we would usually translate:

• Skeggið hans er orðið of langt
  as His beard has become too long or His beard has gotten too long

This construction often emphasizes the resulting state now. The beard is now in the state of being too long.

You will see this pattern a lot:

• Hann er orðinn þreyttur = He has become tired
• Það er orðið kalt = It has gotten cold

Both words agree with skeggið, which is:

• neuter
• singular
• here functioning as the subject

That is why you get neuter singular forms:

• orðið
• langt

The adjective must match the noun it describes or the subject it refers to.

So compare:

• Skeggið er langt = The beard is long
• Hárið er orðið stutt = The hair has become short

Because skegg is neuter, the predicate adjective is langt, not langur.

Here of means too, in the sense of excessively.

So:

• of langt = too long

This Icelandic word is unrelated in meaning to English of.

Compare:

• langt = long
• of langt = too long
• mjög langt = very long

That distinction is important:

• mjög langt = very long, but not necessarily a problem
• of langt = too long, more than is desirable

Because the subject is doing the action to himself.

• raka = to shave
• raka sig = to shave oneself / to shave

In Icelandic, grooming verbs often use a reflexive pronoun where English may simply say shave, wash, dress, and so on.

So:

• hann rakar sig = he shaves / he shaves himself

If you said:

• hann rakar hann

that would usually mean:

• he shaves him
  meaning another male person, not himself

So sig shows that the action comes back to the subject.

Sig is the reflexive pronoun in the accusative.

Icelandic uses reflexive forms when the object refers back to the subject of the same clause.

The main reflexive forms are:

• sig = accusative
• sér = dative
• sín / sitt / sína etc. = possessive reflexive forms

In this sentence, raka takes an accusative object, so the reflexive form is:

• sig

That is why you get:

• hann rakar sig

not sér.

Here svo means so or therefore.

It connects the two ideas:

• his beard has become too long
• so he shaves before the guests arrive

So the sentence structure is:

• Skeggið hans er orðið of langt, svo hann rakar sig ...

This svo works like a coordinating conjunction linking one clause to another consequence/result clause.

Because after svo here, Icelandic is still using a main clause.

Main clauses in Icelandic follow the verb-second principle, meaning the finite verb is in second position inside the clause.

In:

• svo hann rakar sig

the clause itself is:

• hann = first element
• rakar = finite verb in second position
• sig = object

The conjunction svo does not count as the first element of the clause in the same way a sentence-initial adverb would.

So this word order is perfectly normal.

Áður en means before.

It introduces a subordinate clause:

• áður en gestirnir koma = before the guests come / before the guests arrive

You can think of it as:

• áður = earlier, before
• en = than / before introducing the clause

Together they function as a fixed expression meaning before when followed by a clause.

Very common pattern:

• áður en ég fer = before I go
• áður en þau borða = before they eat

Because Icelandic often uses the present tense for future meaning, especially in subordinate clauses like this one.

So:

• áður en gestirnir koma

literally uses present tense, but it means:

• before the guests come / before the guests arrive

English does something very similar:

• I’ll leave before they come
• not usually before they will come

So Icelandic is behaving quite naturally here.

Gestirnir is the definite plural form, meaning the guests.

The noun is:

• gestur = guest

Plural:

• gestir = guests

Definite plural:

• gestirnir = the guests

The sentence is talking about a specific set of guests, not just guests in general, so the definite form is used.

Yes: the word order is different from a main clause with a fronted element.

In this subordinate clause, the order is simply:

• gestirnir = subject
• koma = verb

That is normal subordinate-clause order after áður en.

So the sentence shows a useful contrast:

• svo hann rakar sig = main clause
• áður en gestirnir koma = subordinate clause

This is the kind of pattern you will see all the time in Icelandic sentences with conjunctions.