Af hverju gerir þú þetta svona?

Yes. Af hverju is a very common and natural way to say why in Icelandic.

A few useful notes:

• af hverju = why
• Another common option is hvers vegna, which is a bit more formal or neutral in tone.
• In everyday speech, af hverju is extremely common.

So in this sentence, Af hverju introduces the question just like Why does in English.

Because Icelandic usually changes the word order in direct questions.

In a normal statement, you would usually have:

• Þú gerir þetta svona.
  = You do this like this / this way.

In a question, the finite verb typically comes before the subject:

• Af hverju gerir þú þetta svona?

So this is the normal question pattern:

• question word
• verb
• subject
• the rest of the sentence

This is similar to English Why do you..., where English also changes the normal statement order.

Gerir is the 2nd person singular present tense form of the verb gera (to do, to make).

Here is the relevant part of the present tense:

• ég geri = I do / make
• þú gerir = you do / make
• hann/hún/það gerir = he/she/it does / makes

So gerir þú means do you or are you doing, depending on context.

Because Icelandic does not need a separate dummy do the way English does.

English says:

• Why do you do this?

But Icelandic simply uses the main verb directly:

• Af hverju gerir þú þetta...?

So gerir itself carries the tense and the question structure. There is no extra helping verb equivalent to English do here.

Þetta means this here, and in this sentence it is the direct object of gerir.

That means it is in the accusative case.

More specifically:

• þetta is the neuter singular form of the demonstrative pronoun þessi / þetta
• It refers to this thing, this action, or this situation, depending on context

So in the sentence:

• gerir þú þetta
  = do you do this

Svona means like this, this way, or in this manner.

It describes how something is being done.

So:

• þetta = this
• svona = like this / this way

Together, they give the idea of:

• this, in this way
• or more naturally in English, this this way

In natural English, this often becomes something like:

• Why do you do this like this?
• Why are you doing this this way?
• Why do you do it this way?

They do both relate to this, but they do different jobs in the sentence.

• þetta is a pronoun: it refers to the thing/action itself
• svona is an adverb: it describes the manner, meaning like this / this way

So the structure is roughly:

• gerir þú þetta = do you do this
• gerir þú þetta svona = do you do this like this / this way

They are not redundant, because one is the object and the other describes how the action is carried out.

Yes, absolutely.

That version is:

• Af hverju ertu að gera þetta svona?

This uses the construction:

• vera að + infinitive

That often corresponds to English be doing and emphasizes an action happening right now.

So the difference is roughly:

• Af hverju gerir þú þetta svona?
  = more general, or sometimes present-time depending on context
• Af hverju ertu að gera þetta svona?
  = more clearly Why are you doing this this way right now?

In everyday speech, the vera að version is often very common when talking about something currently happening.

Normally, no. In Icelandic, the subject pronoun is usually kept.

So:

• Af hverju gerir þú þetta svona?
  is normal.

Unlike some languages, Icelandic does not usually drop subject pronouns just because the verb ending already shows the person.

In actual writing and speech, though, you will very often see or hear the pronoun attached to the verb:

• Af hverju gerirðu þetta svona?

That still includes þú; it is just written/spoken in a contracted form.

Because gerirðu is a very common contracted form of gerir þú.

So these mean the same thing:

• Af hverju gerir þú þetta svona?
• Af hverju gerirðu þetta svona?

The contracted form is extremely common in everyday Icelandic, especially in speech and informal writing.

As a learner, it is good to recognize both:

• full form: gerir þú
• contracted form: gerirðu

The letter þ is called thorn, and it is pronounced like the th in thing, not like the th in this.

So:

• þetta begins with the thing sound

A rough pronunciation guide:

• þetta ≈ THET-ta
  with th as in thing

A few other sounds in the sentence:

• hverju: the hv often sounds like a breathy kv-like sound in modern Icelandic
• gerir: the g is pronounced, and the r is an Icelandic r
• svona: roughly SVOH-na

Exact pronunciation depends somewhat on accent and speaking speed, but recognizing þ = th in thing is the most important point here.

It depends a lot on tone of voice and context.

By itself, Af hverju gerir þú þetta svona? can be:

• a genuine question
• a request for explanation
• mildly critical
• even annoyed, depending on how it is said

That is similar to English. Compare:

• Why do you do it this way?
  This can sound curious or critical depending on tone.

So grammatically the sentence is neutral, but pragmatically it can easily sound like criticism if spoken sharply.

You could use other words, but svona is very natural.

A common alternative is þannig:

• Af hverju gerir þú þetta þannig?

Both can mean like that / in that way, though there can be small differences in feel depending on context.

Very roughly:

• svona often feels like like this / like that, in this sort of way
• þannig often feels a bit more like in that way / in such a way

In many everyday situations, they overlap a lot. For this sentence, svona is completely idiomatic.