Ég skrifa þetta ekki með penna í dag; ég nota blýant og strokleður.

Because that is the natural word order here. In Icelandic, ekki usually comes after the finite verb, but short object words such as þetta, það, hann, and so on often come before ekki.

So:

• Ég skrifa þetta ekki = neutral, natural
• Ég skrifa ekki þetta = more contrastive, like I’m not writing this (maybe something else)

That makes þetta ekki a very common pattern.

Here þetta is the direct object of skrifa, so it is in the accusative.

A useful detail is that for this word, the neuter singular nominative and accusative have the same form: þetta. So even though the case is accusative here, the word still looks the same.

Because með takes the accusative case.

The noun is:

• penni = nominative singular
• penna = accusative singular

So með penna is the correct form. In this sentence, með penna means using a pen.

Here it means using a tool/instrument.

So með penna means with a pen / using a pen, not together with a pen in some literal companionship sense. Icelandic uses með for this kind of instrumental meaning very naturally.

Because Icelandic does not have an indefinite article like English a/an.

So:

• penni can mean a pen
• blýantur can mean a pencil
• strokleður can mean an eraser

If you want to say the, Icelandic normally adds it to the end of the noun:

• penninn = the pen
• blýanturinn = the pencil

So the bare nouns in this sentence are perfectly normal for a pen, a pencil, and an eraser.

Because both nouns are objects of nota, so they are in the accusative. But different nouns change differently.

• blýantur is a masculine noun:

  • nominative: blýantur
  • accusative: blýant

• strokleður is a neuter noun:

  • nominative: strokleður
  • accusative: strokleður

So blýantur changes form, while strokleður does not.

Because the second clause uses a different structure.

• skrifa með penna = write with a pen
• nota blýant og strokleður = use a pencil and an eraser

The verb nota takes a direct object, so no preposition is needed there.

You certainly could make a sentence with með blýanti, but that would be a different grammatical structure. Here the sentence is specifically saying I use a pencil and an eraser.

Because the semicolon links two independent clauses, and each clause normally needs its own subject.

So the sentence is:

• Ég skrifa þetta ekki með penna í dag
• ég nota blýant og strokleður

Even though the subject is the same person in both clauses, Icelandic normally keeps the subject explicit here. It does not usually drop ég the way some languages do.

Í dag is the normal Icelandic expression for today.

It is best learned as a fixed time expression. Even though í often has meanings like in or into, in í dag the whole phrase simply functions as an adverbial expression of time: today.

You can also move it in the sentence:

• Í dag skrifa ég þetta ekki með penna.

That is also correct.

Yes, but Icelandic has an important rule: in a main clause, the finite verb usually stays in second position.

So these are possible:

• Ég skrifa þetta ekki með penna í dag.
• Í dag skrifa ég þetta ekki með penna.

Notice that when Í dag moves to the front, skrifa still comes second, and ég moves after it.

This is different from normal English word order and is one of the most important patterns in Icelandic.

Yes, the semicolon is normal here. It connects two closely related clauses without making them two completely separate sentences.

Because a semicolon does not begin a new sentence, the next word is not automatically capitalized. So:

• ... í dag; ég nota ...

is exactly what you would expect.

A full stop would also be possible, but the semicolon shows the two thoughts are tightly connected.

A native English speaker often notices these right away:

• þ is like th in thing
• ð is like th in this

So in this sentence:

• þetta starts with the thing sound
• með has the this sound at the end

These letters are very common in Icelandic, so getting used to them early helps a lot.