Hann er venjulega kurteis, en í dag er hann þreyttur og smá ókurteis.

Because en í dag er hann þreyttur og smá ókurteis is a new clause, and Icelandic normally states the subject again in a new finite clause.

So the sentence is really:

• Hann er venjulega kurteis
• en í dag er hann þreyttur og smá ókurteis

In English, we also usually repeat he here: He is usually polite, but today he is tired and a little rude.

This is because Icelandic follows a verb-second pattern in main clauses.

That means:

• one element comes first
• the finite verb usually comes second

So if í dag is placed first for emphasis, the verb er must come next:

• Í dag er hann þreyttur

Not:

• Í dag hann er þreyttur

This is a very important Icelandic word-order rule.

Venjulega means usually.

In this sentence, it comes after er:

• Hann er venjulega kurteis

That is a very natural position for an adverb like this in Icelandic. It modifies the whole statement and shows that this is his normal behavior.

You can also sometimes move it for emphasis:

• Venjulega er hann kurteis

Both are correct, but the original word order is very natural and common.

All three words are adjectives, but Icelandic adjectives do not all look the same in the masculine singular.

Here, the subject is hann (he), so the adjectives are in masculine singular nominative because they describe the subject after er.

• kurteis = polite
• þreyttur = tired
• ókurteis = rude / impolite

The important point is that adjectives must agree with the person or thing they describe, but different adjectives can have different endings in the same grammatical form. So þreyttur has -ur, while kurteis does not.

Here smá means a little, slightly, or kind of.

So:

• smá ókurteis = a little rude / slightly impolite

In everyday Icelandic, smá is often used informally as an adverb like this. It softens the adjective a bit, just like English a bit or a little.

Yes, very much so.

The prefix ó- often gives a negative meaning, similar to English un-, in-, or im-.

So:

• kurteis = polite
• ókurteis = impolite / rude

This is a very useful pattern in Icelandic, and you will see ó- in many words.

Because dagur is the dictionary form, but after the preposition í in this expression, the noun appears as dag.

So:

• dictionary form: dagur = day
• in the phrase: í dag = today

This is a fixed and very common time expression in Icelandic. Learners usually just memorize í dag as the normal way to say today.

No, not with different verbs.

Icelandic uses vera (to be) for both:

• general qualities: Hann er venjulega kurteis
• temporary conditions: í dag er hann þreyttur

So unlike languages that split to be into two verbs, Icelandic uses the same verb and lets context do the work.

In this sentence, the contrast between venjulega (usually) and í dag (today) clearly shows:

• his normal behavior
• his temporary state today

Yes.

You can say:

• Venjulega er hann kurteis

That means the same thing as:

• Hann er venjulega kurteis

The difference is mainly one of emphasis and style. Putting venjulega first highlights the idea of usually more strongly.

Because of verb-second word order, if venjulega comes first, er must still come second:

• Venjulega er hann kurteis

not:

• Venjulega hann er kurteis

The letter þ is pronounced like the th in think, not like the th in this.

So þreyttur begins with that voiceless th sound.

A rough English-friendly guide for þreyttur is:

• THRAYT-tur

That is only approximate, but it helps.

A few useful pronunciation notes:

• þ = th in think
• ey here sounds roughly like ay in say
• the r is an Icelandic r, not an English one

Because en means but, and it joins two contrasting clauses.

The comma helps show the break between:

• Hann er venjulega kurteis
• en í dag er hann þreyttur og smá ókurteis

This is very similar to English punctuation in a sentence like:

• He is usually polite, but today he is tired and a little rude.

Because there are two separate clauses, and each clause needs its own verb.

So we have:

• Hann er venjulega kurteis
• en í dag er hann þreyttur og smá ókurteis

You cannot normally leave out the second er here. Icelandic needs the verb in the second clause just as English does.