Vináttan okkar helst sterk þegar við tölum saman á hverjum degi.

Vináttan is the definite form of vinátta (friendship), so it literally means the friendship.

In Icelandic, it is very natural to use the definite noun together with a following possessive, so vináttan okkar means our friendship. The idea is not just friendship in general, but a specific friendship that belongs to us.

So:

• vinátta = friendship
• vináttan = the friendship
• vináttan okkar = our friendship

Okkar is the genitive plural form of við (we/us) and is used to mean our.

With okkar, ykkar, and þeirra, Icelandic very often puts the possessive after the noun:

• vináttan okkar = our friendship
• húsið þeirra = their house

That is the most neutral word order here. Putting it before the noun, okkar vinátta, is possible, but it sounds more marked or emphatic.

A useful thing to remember: okkar does not change to match the gender or number of the noun. It just stays okkar.

Here, helst is a verb, not an adverb. It means stays, remains, or keeps.

It is the 3rd person singular present form of haldast.

So:

• vináttan okkar helst sterk = our friendship stays/remains strong

This is easy to confuse with the other word helst, which can also mean preferably or rather. In this sentence, though, it is clearly the verb because it is the main action of the sentence.

Because sterk is a predicate adjective here: it comes after the verb and describes the subject.

In vináttan okkar helst sterk, the word sterk describes vináttan. Predicate adjectives in Icelandic agree with the noun in gender, number, and case:

• vináttan is feminine, singular, nominative
• so the adjective is sterk

Compare:

• sterk vinátta = strong friendship
• hin sterka vinátta = the strong friendship
• vináttan er sterk = the friendship is strong

So sterka would fit in other structures, but not in this one.

Þegar means when, while ef means if.

This sentence describes something that happens as a regular or expected pattern, so þegar is the right choice:

• þegar við tölum saman á hverjum degi = when we talk to each other every day

If you used ef, the meaning would become more conditional:

• ef við tölum saman... = if we talk...

So þegar fits the idea of a real, recurring situation better.

Við tölum means we talk or we speak.

Saman literally means together, but in this expression tala saman is a very common way to say talk together, talk to each other, or have a conversation.

So:

• við tölum = we speak / we talk
• við tölum saman = we talk together / we talk to each other

The sentence would still be grammatical without saman, but tala saman sounds more natural when the idea is mutual conversation.

Á hverjum degi means every day, literally something like on each day.

Both hverjum and degi are in the dative singular:

• dagur = day
• degi = dative singular of dagur
• hverjum = dative singular of hver (each/every)

This happens because the preposition á often takes the dative in time expressions like this.

So the structure is:

• á + dative
• á hverjum degi = every day

You may also see other ways to express this idea, such as hvern dag or daglega, but á hverjum degi is perfectly natural.

Yes. You can also say:

Þegar við tölum saman á hverjum degi, helst vináttan okkar sterk.

That is fully grammatical.

The important thing is that Icelandic then follows its usual V2 pattern in the main clause: after the fronted subordinate clause, the finite verb comes before the subject:

• Þegar við tölum saman á hverjum degi, helst vináttan okkar sterk.

Not:

• Þegar við tölum saman á hverjum degi, vináttan okkar helst sterk. ← not correct as neutral standard word order

Because they do two different jobs:

• okkar = our; it belongs to the noun phrase vináttan okkar (our friendship)
• við = we; it is the subject of the clause við tölum saman (we talk together)

So even though both refer to the same people, they are not interchangeable.

Compare:

• vináttan okkar = our friendship
• við tölum saman = we talk to each other

One shows possession; the other shows who is doing the action.