Mér tókst að skrá mig inn í netbankann í morgun.

Because takast is commonly used in an impersonal construction in Icelandic.

With this verb, the person who succeeds is often put in the dative case, so:

• mér = to/for me
• þér = to/for you
• honum = to/for him

So mér tókst að... literally works more like:

• it succeeded for me to...

Natural English translates that as:

• I managed to...
• I succeeded in...

So even though English uses I, Icelandic uses mér here.

Tókst is the past tense of takast.

In this sentence, takast means:

• to succeed
• to manage
• to work out

So mér tókst að skrá mig inn means:

• I managed to log in
• I succeeded in logging in

A useful pair to remember is:

• mér tekst = I manage / I succeed
• mér tókst = I managed / I succeeded

Because Icelandic does not need a dummy subject here the way English sometimes does.

English might use something like:

• It worked
• I managed

But Icelandic can simply say:

• Mér tókst að...

The construction is complete without það. The idea being expressed is that the action in the infinitive clause — að skrá mig inn í netbankann — was successful.

They are similar, but not identical.

• ég gat... = I could... / I was able to...
• mér tókst að... = I managed to... / I succeeded in...

Mér tókst að... often suggests that the action may have involved some difficulty, effort, or uncertainty.

So this sentence can sound a bit like:

• I finally managed to log into the online bank this morning
• I succeeded in logging in this morning

If you used ég gat skráð mig inn, that would focus more on ability or possibility, not so much on successful outcome.

Because að is the normal marker for the infinitive in Icelandic, like to in English.

So:

• að skrá = to register / to log
• að skrá mig inn = to log myself in
• að skrá mig inn í netbankann = to log myself into the online bank

After takast, Icelandic very often uses að + infinitive:

• Mér tókst að finna lykilinn.
• Mér tókst að ná sambandi.

So the pattern is very common.

Good question. In Icelandic, sig is only used for the third person.

So:

• ég → mig
• þú → þig
• hann/hún/það → sig

That means:

• Ég skrái mig inn = I log in
• Þú skráir þig inn = you log in
• Hann skráir sig inn = he logs in

So in your sentence, mig is correct because the person involved is first person.

Literally, it is something like:

• register me in
• sign me in

But in modern usage, skrá sig inn is a standard way to say:

• log in
• sign in

So even if the literal wording feels strange to an English speaker, it is a normal Icelandic expression for accessing an account or system.

Because they do different jobs.

• inn is an adverb meaning in / inside / inward
• í is a preposition meaning in / into

In expressions like skrá sig inn í they work together, very much like English log in to.

So:

• skrá mig inn = log me in
• skrá mig inn í netbankann = log me into the online bank

This combination can feel redundant to English speakers at first, but it is very natural in Icelandic.

Because netbankann is:

• accusative singular
• definite form
• of the masculine noun netbanki

Here is the basic pattern:

• netbanki = an online bank / the online bank (dictionary form, nominative singular)
• netbankann = the online bank (accusative singular definite)

It is accusative here because í takes the accusative when it expresses motion or direction into something.

Compare:

• í netbankann = into the online bank → accusative
• í netbankanum = in the online bank → dative, location

So the sentence is treating logging in as movement into the system.

Because í morgun is a fixed Icelandic time expression meaning:

• this morning

It does not mean just any morning. It specifically refers to the morning of today.

Some useful comparisons:

• í morgun = this morning
• í gær = yesterday
• á morgun = tomorrow

So í morgun is just an idiomatic expression you should learn as a whole chunk.

Yes. Icelandic word order is flexible, but the finite verb in a main clause normally stays in the second position.

Your sentence is:

• Mér tókst að skrá mig inn í netbankann í morgun.

You could also say:

• Í morgun tókst mér að skrá mig inn í netbankann.

That still follows the same rule:

• first element: Í morgun
• second element: tókst

So the meaning stays basically the same, but the emphasis changes slightly. Starting with Í morgun puts more focus on the time.

Yes, it is very natural.

A native speaker would understand it immediately as something like:

• I managed to log into the online bank this morning.

It sounds especially natural if the speaker is implying that logging in was not completely straightforward — for example, there may have been a password issue, technical trouble, or some earlier failed attempts.

That is one reason mér tókst að... is a very useful pattern to learn.