Ég athuga samninginn vandlega áður en ég undirrita hann.

Because athuga takes a direct object, and that object goes in the accusative case.

• samningur = a contract / the contract in the nominative form
• samninginn = the contract in the accusative singular

So in this sentence:

• Ég athuga samninginn = I check the contract

The ending -inn is the suffixed definite article, so samninginn means the contract, not just a contract.

The dictionary form is samningur.

Here are the important forms:

• samningur = nominative singular
• samning = accusative singular without the article
• samninginn = accusative singular with the

So samninginn is built from the noun stem plus the definite article. Icelandic usually attaches the to the end of the noun instead of using a separate word like English.

Hann means him/it here, and it refers back to samninginn.

Since samningur is a masculine noun in Icelandic, the pronoun that refers to it is masculine too:

• samningur = masculine noun
• hann = him/it in the accusative masculine singular

In English we would normally say sign it, but Icelandic uses the grammatical gender of the noun, so hann is completely natural.

Because Icelandic normally states the subject explicitly with each finite verb.

So:

• Ég athuga ...
• áður en ég undirrita ...

Both verbs, athuga and undirrita, have their own subject, and Icelandic does not usually drop subject pronouns the way some other languages do.

Even though English sometimes avoids repetition stylistically, Icelandic often keeps it.

Áður en means before when it introduces a clause.

In this sentence:

• áður en ég undirrita hann = before I sign it

You can think of it as a fixed expression:

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

It is very commonly used before a full clause with a verb.

Compare:

• áður en ég fer = before I go
• áður en hún byrjar = before she starts

Icelandic subordinate clauses often look quite similar to main clauses in basic subject-verb order, especially in simple examples like this one.

So:

• ég undirrita hann = subject + verb + object

That is normal after áður en.

What often changes more noticeably is the word order in the main clause if the subordinate clause comes first. For example:

• Áður en ég undirrita hann, athuga ég samninginn vandlega.

Here the main clause becomes athuga ég..., with the verb before the subject, because something else has been placed first in the sentence.

Athuga is the present tense, first person singular:

• ég athuga = I check / I examine

It comes from the verb að athuga.

This present tense can describe:

• a habitual action: I check the contract carefully before I sign it
• a general procedure
• something happening now, depending on context

So the Icelandic present tense works a lot like the English present here.

Undirrita is also present tense, first person singular:

• ég undirrita = I sign

The infinitive is að undirrita.

So the sentence contains two present-tense verbs:

• ég athuga
• ég undirrita

That is normal in Icelandic when describing a routine or general sequence of actions.

Vandlega means carefully, and it is an adverb.

It describes how the checking is done:

• Ég athuga samninginn vandlega = I check the contract carefully

A useful pattern to notice is:

• adjective: vandlegur = careful / thorough
• adverb: vandlega = carefully / thoroughly

Many Icelandic adverbs are formed with -lega, similar to English -ly in many cases.

That word order is very natural in Icelandic.

The structure is:

• Ég = subject
• athuga = verb
• samninginn = object
• vandlega = adverb
• áður en... = subordinate clause

So the sentence goes:

• subject
• verb
• object
• adverb
• time clause

You can sometimes move adverbs around for emphasis, but athuga samninginn vandlega is a very normal and idiomatic order.

Yes. Athuga means check, examine, look over, and it fits very well here. But depending on nuance, other verbs can also appear in similar contexts.

For example:

• skoða often means look at / inspect / examine
• lesa yfir means read over
• fara yfir means go over / review

Still, athuga samninginn vandlega is a very natural way to say that you check the contract carefully before signing it.

Because Icelandic often uses the present tense for general truths, routines, and planned or expected actions, just like English can.

This sentence sounds like a general procedure:

• I check the contract carefully before I sign it

It is not necessarily talking about one specific future event. It describes what the speaker does as a rule.

If the context were strongly future-oriented, Icelandic could express that too, but the present tense is completely normal here.

If you start with the subordinate clause, the main clause usually shows inversion:

• Áður en ég undirrita hann, athuga ég samninginn vandlega.

Notice the change:

• normal main clause: Ég athuga...
• after a fronted clause: athuga ég...

This is a very important Icelandic pattern: when something other than the subject comes first, the finite verb typically comes in the second position.