Hvort sem það rignir eða ekki, tek ég regnjakka með mér.

Hvort sem means whether in the pattern whether ... or not.

So:

• Hvort sem það rignir eða ekki = Whether it rains or not

This expression introduces a clause that says the result is the same in either case.

A very common pattern is:

• Hvort sem + clause + eða ekki, ...
• Whether + clause + or not, ...

Together they make the full structure whether X or not.

Breakdown:

• hvort sem = whether
• það rignir = it rains / it is raining
• eða ekki = or not

So the whole first part literally works like:

• whether it rains or not

In Icelandic, this combination is very normal and idiomatic.

Here það is a dummy subject, just like it in English weather expressions.

Examples:

• Það rignir. = It is raining.
• Það snjóar. = It is snowing.

Just as English says it rains even though it does not refer to a real thing, Icelandic uses það in the same way.

So in this sentence, það does not point to a specific object; it is simply required by the grammar of the weather expression.

Rignir is the 3rd person singular present tense of the verb að rigna (to rain).

So:

• að rigna = to rain
• það rignir = it rains / it is raining

Because the subject is það (it), the verb is in the 3rd person singular form.

This is because Icelandic usually follows a verb-second (V2) word-order rule in main clauses.

The first element in the sentence is the subordinate clause:

• Hvort sem það rignir eða ekki

After that, the finite verb of the main clause comes next:

• tek

Then the subject:

• ég

So:

• Hvort sem það rignir eða ekki, tek ég regnjakka með mér.

This is similar to how some English structures invert after a fronted phrase, though Icelandic does this much more regularly.

A simpler comparison:

• Ég tek regnjakka með mér. = I take a rain jacket with me.
• Á morgun tek ég regnjakka með mér. = Tomorrow I take a rain jacket with me.

When something else comes first, the verb typically comes before the subject.

In standard Icelandic, that would usually be considered incorrect or at least nonstandard, because it breaks the normal verb-second pattern.

The standard form is:

• Hvort sem það rignir eða ekki, tek ég regnjakka með mér.

So after the opening clause, the verb tek should come before ég.

Because regnjakka is the accusative singular form, used here as the direct object of tek (take).

The noun is:

• regnjakki = rain jacket (nominative singular)

But after tek in this sentence, it is the thing being taken, so it appears in the accusative:

• tek regnjakka = take a rain jacket

So:

• regnjakki = dictionary/basic form
• regnjakka = object form used here

Með mér means with me.

The preposition með often takes the dative case, and the dative form of ég (I) is mér.

So:

• ég = I
• mig = me (accusative)
• mér = me (dative)

Since með is followed here by the dative, you get:

• með mér = with me

In the full sentence:

• tek ég regnjakka með mér = I take a rain jacket with me

Yes, very often taka ... með sér means to take ... along / to take ... with oneself.

Examples:

• Ég tek bókina með mér. = I’m taking the book with me.
• Hún tekur nesti með sér. = She takes food with her.

Notice that the pronoun changes depending on the subject:

• með mér = with me
• með þér = with you
• með sér = with himself/herself/itself/themselves

So in your sentence, tek ég regnjakka með mér is a very natural way to say I take a rain jacket with me.

It can often cover both ideas, depending on context.

Icelandic present tense is commonly used for:

• general/habitual meaning
• present or near-future meaning
• sometimes a decision or regular practice

So this sentence could mean something like:

• I take a rain jacket with me
• I’ll take a rain jacket with me
• I always take a rain jacket with me

The exact nuance depends on the situation.

Either can work, depending on context.

• það rignir can mean it rains or it is raining
• In this sentence, English usually prefers Whether it rains or not...

So the most natural translation of the whole sentence is:

• Whether it rains or not, I take a rain jacket with me.

But grammatically, the Icelandic present tense itself is not limited to only one English tense.

Yes.

Hvort by itself often introduces an indirect whether question:

• Ég veit ekki hvort það rignir.
• I don’t know whether it is raining.

Hvort sem is more like whether ... or not / regardless of whether:

• Hvort sem það rignir eða ekki, ...
• Whether it rains or not, ...

So hvort sem is especially used when the result is the same no matter which possibility is true.

Yes. That is a good translation of the meaning.

Hvort sem ... eða ekki often has the sense of:

• whether ... or not
• regardless of whether ...

So this sentence means that rain does not affect the speaker’s decision: the rain jacket comes along either way.

A rough English-friendly guide would be something like:

• hvort sem thath RIG-nir EH-tha EHK-ki

A few useful notes:

• þ is pronounced like th in this or thing depending on context; here það is roughly thath
• ð is also a voiced th sound
• rignir begins with rig-, not with a silent g
• ekki is roughly ehk-ki

This is only an approximation, but it can help you get started.

Yes, several useful things:

1. Weather expressions use a dummy subject

   • það rignir = it rains

2. Icelandic often uses verb-second word order

   • after a fronted clause: tek ég, not ég tek

3. Objects change form by case

   • regnjakki → regnjakka

4. Prepositions affect pronoun forms

   • með mér uses the dative mér

5. Present tense can be flexible in meaning

   • it may correspond to take, am taking, or will take, depending on context

So although the sentence is short, it shows several very central features of Icelandic grammar.