Hún las um samsköttunina í ljósi þess að skattskyldan breyttist.

Because lesa is a strong verb, not a regular weak verb.

• Infinitive: lesa = to read
• Past tense, 3rd person singular: las = read

So Hún las means She read.

Many common Icelandic verbs form the past tense by changing the vowel rather than adding a regular ending. This is similar to English verbs like sing → sang or drive → drove.

Because um normally takes the accusative case, and samsköttunina is the accusative definite singular form of the noun.

So the structure is:

• lesa um ... = to read about ...
• samsköttun = joint taxation / fiscal consolidation
• samsköttunina = the joint taxation, in the accusative

A learner-friendly way to think of it is:

• um tells you what the reading is about
• the noun after um must go into the accusative

Yes, very often.

• lesa by itself usually means read something directly:
  • lesa bók = read a book
• lesa um means read about a topic:
  • lesa um skatta = read about taxes

So in your sentence, las um samsköttunina means she was reading on the subject of that topic, not necessarily reading the topic itself as a physical object.

It is a common expression meaning something like:

• in light of the fact that
• considering that
• given that

It is best learned as a unit.

Literally, it is built from:

• í ljósi = in the light
• þess að = of that / that

But in normal English you should not translate it word for word. Treat í ljósi þess að as a fixed linking phrase that introduces a reason or relevant circumstance.

Þess is the genitive form of það.

In the expression í ljósi þess að, it appears because í ljósi is followed by a genitive element. So this is not random: the grammar of the expression requires it.

You can think of the pattern as:

• í ljósi þess að + clause

For example:

• í ljósi þess að skattskyldan breyttist

It does not necessarily refer back to a specific earlier noun. In this construction, it is mostly part of the fixed phrase.

Here að is a conjunction meaning that, not the infinitive marker to.

So:

• í ljósi þess að skattskyldan breyttist = in light of the fact that the tax liability changed

This að introduces a whole clause:

• skattskyldan breyttist

That is different from examples like:

• að lesa = to read

where að is the infinitive marker.

Because skattskyldan is the subject of breyttist, so it is in the nominative case.

The base noun is:

• skattskylda = tax liability / tax obligation

The definite nominative singular form is:

• skattskyldan = the tax liability

So here:

• skattskyldan breyttist = the tax liability changed

It is not an object, so it does not go into the accusative here.

Breyttist is the past tense of breytast, which means to change or to undergo a change.

The -st ending is very common in Icelandic and is often called the middle voice ending. In many cases, it gives an intransitive or reflexive-like meaning.

Compare:

• breyta einhverju = to change something
• eitthvað breytist = something changes

So:

• Hún breytti reglunum = She changed the rules
• Reglurnar breyttust = The rules changed

In your sentence:

• skattskyldan breyttist = the tax liability changed

This is a subordinate clause introduced by að.

In the clause:

• skattskyldan = subject
• breyttist = verb

So the order is simply subject + verb.

That is the normal, neutral order here. Icelandic main clauses often show verb-second behavior, but subordinate clauses introduced by words like að do not follow the same pattern in the same way.

So:

• Main clause: Hún las ...
• Subordinate clause: að skattskyldan breyttist

This is completely normal.

In Icelandic, the definite article is very often attached to the end of the noun instead of being a separate word like the in English.

So:

• samsköttun = joint taxation
• samsköttunin = the joint taxation
• samsköttunina = the joint taxation, accusative

And:

• skattskylda = tax liability
• skattskyldan = the tax liability

The exact ending changes depending on:

• gender
• number
• case

That is why the article does not look the same in both words.

Yes. Icelandic very often builds long meanings by combining smaller parts into compounds.

For example:

• skattskylda
  • skatt- = tax
  • skylda = obligation, duty
  • together: tax liability / tax obligation

And in samsköttun:

• sam- means together / joint
• the rest is related to taxation

So even if a word looks intimidating, it often contains familiar building blocks. That is one reason Icelandic vocabulary can become easier over time: once you know the pieces, you can often make educated guesses.

Not exactly.

• vegna þess að usually means a straightforward because
• í ljósi þess að is more like in light of the fact that, considering that, or given that

So í ljósi þess að often sounds a bit more formal and slightly more analytical. It suggests that the following fact is something being taken into account, not just a simple cause.

In this sentence, the idea is not only because the tax liability changed, but more with that change in mind or in view of that change.