Hann er svo þrjóskur að hann vill gera þetta sjálfur, jafnvel þegar hann er of þreyttur.

Svo ... að means so ... that.

So:

• Hann er svo þrjóskur að ... = He is so stubborn that ...

This is a very common Icelandic pattern:

• svo stór að = so big that
• svo þreyttur að = so tired that
• svo fljótur að = so fast that

Here, svo intensifies the adjective, and að introduces the result clause.

Because þrjóskur agrees with hann.

In this sentence, hann is:

• masculine
• singular
• nominative

So the adjective appears in the masculine singular nominative form:

• þrjóskur = stubborn (masculine singular nominative)

This is the form used after er when describing hann:

• Hann er þrjóskur = He is stubborn

Compare:

• Hún er þrjósk = She is stubborn
• Það er þrjóskt = It is stubborn
• Þeir eru þrjóskir = They are stubborn

Because vill is the present tense singular form of the verb vilja (to want).

The infinitive is:

• að vilja = to want

But with hann in the present tense, you say:

• hann vill = he wants

This verb is irregular, so learners usually have to memorize its forms.

A few useful forms:

• ég vil = I want
• þú vilt = you want
• hann/hún/það vill = he/she/it wants
• við viljum = we want

So hann vill gera þetta means he wants to do this.

Because the clause after að needs its own subject.

The sentence is made of two parts:

1. Hann er svo þrjóskur
2. að hann vill gera þetta sjálfur

In English, you also repeat the subject:

• He is so stubborn that he wants to do this himself

Icelandic normally does the same here. The second clause is a full clause, so it needs hann.

It means do this himself.

Breaking it down:

• gera = do, make
• þetta = this
• sjálfur = self / himself

So:

• hann vill gera þetta sjálfur = he wants to do this himself

Here sjálfur adds emphasis. It means he wants to do it personally, on his own, without help.

Because sjálfur agrees with the person it refers to, here hann.

So again, because the subject is masculine singular nominative, the form is:

• sjálfur = himself

Compare:

• Ég geri þetta sjálfur = I do this myself. (said by a man)
• Ég geri þetta sjálf = I do this myself. (said by a woman)
• Hún gerir þetta sjálf = She does this herself

Even though English uses myself/himself/herself, Icelandic uses forms of sjálfur that agree grammatically.

If you remove sjálfur, the sentence still means he wants to do it, but the idea of personally / by himself becomes weaker or disappears.

Compare:

• hann vill gera þetta = he wants to do this
• hann vill gera þetta sjálfur = he wants to do this himself

So sjálfur adds emphasis: not someone else, not with help, but he himself.

Jafnvel þegar means even when.

Breaking it down:

• jafnvel = even
• þegar = when

So:

• jafnvel þegar hann er of þreyttur = even when he is too tired

This adds a stronger sense of contrast: he still wants to do it himself, even in situations where it would make sense not to.

Here of means too in the sense of excessively.

So:

• of þreyttur = too tired

This is the same idea as in English:

• of stór = too big
• of seinn = too late
• of erfitt = too difficult

Be careful: this of is not the English word of. It is an Icelandic adverb meaning too, excessively.

For the same reason as þrjóskur: it agrees with hann.

In:

• hann er of þreyttur = he is too tired

the adjective describes hann, so it appears in the masculine singular nominative form:

• þreyttur = tired (masculine singular nominative)

Compare:

• hún er of þreytt = she is too tired
• þeir eru of þreyttir = they are too tired

Because after a subordinating word like þegar (when), Icelandic normally uses subordinate clause word order, where the subject comes before the finite verb.

So:

• þegar hann er of þreyttur = when he is too tired

This is normal subordinate clause order.

Learners often notice that Icelandic main clauses often have verb-second word order, but subordinate clauses usually do not. Compare:

• Hann er of þreyttur. = He is too tired.
• ... þegar hann er of þreyttur. = ... when he is too tired.

So this word order is exactly what you should expect after þegar.

Þetta means this, and here it is the object of gera.

So:

• gera þetta = do this

It points to some specific task, action, or thing already understood from context.

A few related forms learners often meet are:

• þetta = this
• það = that / it
• þessu = this (dative form)
• þessum = this/these (in certain forms)

In this sentence, you can simply understand þetta as the direct object: the thing he wants to do.

The adjectives and sjálfur would change form to agree with a feminine subject.

You would get:

• Hún er svo þrjósk að hún vill gera þetta sjálf, jafnvel þegar hún er of þreytt.

Changes:

• hann → hún
• þrjóskur → þrjósk
• sjálfur → sjálf
• þreyttur → þreytt

This is a very important feature of Icelandic: adjectives and words like sjálfur change according to gender, number, and case.

No. Here að is a conjunction meaning that.

In Icelandic, að can have different jobs:

1. Conjunction: that

   • Hann er svo þrjóskur að ...
   • He is so stubborn that ...

2. Infinitive marker: to

   • að gera = to do

So this sentence contains both ideas, but only one actual að is written:

• ... að hann vill gera þetta sjálfur

Here the written að is the conjunction that.
The verb gera is an infinitive after vill, and Icelandic does not need an extra infinitive marker there.

It helps separate the extra subordinate idea at the end:

• ..., jafnvel þegar hann er of þreyttur.

In practice, the comma marks a pause and makes the structure clearer. The final part adds extra information about when this happens.

For a learner, the most important thing is not punctuation but structure:

• main statement: Hann er svo þrjóskur að hann vill gera þetta sjálfur
• added subordinate clause: jafnvel þegar hann er of þreyttur

So the comma is natural and helpful here.