Vi skal nok skåle, når alle er kommet, og bagefter vil jeg lykønske min søster.

Not exactly. Skal nok often means something like will surely, will definitely, or will be fine / will happen depending on context.

In this sentence, Vi skal nok skåle means more than a neutral we will toast. It suggests reassurance or confidence:

• We’ll definitely have a toast
• We’ll make sure to toast
• We’ll toast, don’t worry

So nok adds a nuance of certainty or reassurance.

At skåle specifically means to make a toast or to say cheers / raise glasses. It is more specific than at drikke, which just means to drink.

So:

• Vi skåler = We make a toast / say cheers
• Vi drikker = We drink

If people are celebrating and raising glasses together, skåle is the natural verb.

Når is used for something expected to happen in the future, especially when when means at the time that.

So:

• når alle er kommet = when everyone has arrived

This is different from:

• da = when for a specific event in the past
• hvis = if

Examples:

• Når han kommer, spiser vi. = When he comes, we eat / will eat.
• Da han kom, spiste vi. = When he came, we were eating / ate.
• Hvis han kommer, spiser vi. = If he comes, we eat / will eat.

Here, the arrival is expected, so når is the right choice.

Danish often uses the present perfect after når when it wants to show that one future action happens after another action has been completed.

So:

• når alle er kommet literally looks like when everyone has come / has arrived
• natural English meaning: when everyone has arrived

This emphasizes completion: first everyone arrives, then the toast happens.

Compare:

• Når alle kommer = when everyone comes / as everyone comes
• Når alle er kommet = when everyone has arrived

The second one fits this sentence better because the toast happens only after the arrival is complete.

Because komme is one of the Danish verbs that normally forms the perfect tense with være in older and still standard usage in this kind of sentence:

• er kommet = has/have come, has/have arrived

This is similar to older German patterns and some other European languages where verbs of movement often take to be rather than to have.

So:

• alle er kommet = everyone has arrived

That is the standard form you should learn here.

This is because Danish is a V2 language in main clauses. That means the finite verb must come in the second position.

The clause is:

• bagefter = first element
• vil = finite verb in second position
• jeg = subject after the verb

So:

• Bagefter vil jeg lykønske min søster.

If the sentence started with the subject, it would be:

• Jeg vil lykønske min søster bagefter.

Both are possible, but when bagefter is moved to the front, the verb must come before the subject.

Bagefter means afterward / afterwards / later. It refers to what happens next, after something already mentioned.

In this sentence:

• first: everyone arrives
• then: people toast
• after that: I will congratulate my sister

So bagefter links the second action to the earlier one.

Efter usually needs an object:

• efter festen = after the party
• efter middagen = after dinner

But bagefter can stand on its own:

• Vi spiser, og bagefter går vi hjem. = We eat, and afterward we go home.

At lykønske means to congratulate.

So:

• jeg vil lykønske min søster = I want to / will congratulate my sister

Tillykke! is the expression Congratulations! or Happy birthday! depending on context.

So the difference is:

• lykønske nogen = the verb to congratulate someone
• tillykke = the set phrase you say

Example:

• Jeg lykønskede hende og sagde tillykke.
• I congratulated her and said congratulations.

Danish usually uses a possessive when talking about a family member in this kind of context:

• min søster = my sister
• min mor = my mother
• min bror = my brother

Using just søster by itself would not sound natural here. You normally need:

• an article: en søster
• or a possessive: min søster

Since the speaker means a specific sister, min søster is the natural choice.

It can potentially suggest either, because vil can mean both will and want to, depending on context.

Here, the most natural reading is future:

• bagefter vil jeg lykønske min søster = afterward I’ll congratulate my sister

But there is also a slight sense of intention or willingness, which is very common with vil in Danish. So it can feel like:

• afterward I intend to congratulate my sister

This overlap is normal in Danish.

This follows standard Danish comma conventions.

• Vi skal nok skåle, når alle er kommet, ...

  • the når-clause is a subordinate clause, so it is set off with commas in standard Danish spelling

• ..., og bagefter vil jeg lykønske min søster.

  • og joins two main clauses:
    • Vi skal nok skåle ...
    • bagefter vil jeg lykønske min søster

So the commas help show the sentence structure clearly.

Very natural already. In speech, the speaker might reduce or soften some parts, but the structure is completely normal.

A few spoken-style alternatives could be:

• Vi skal nok skåle, når alle er kommet, og så vil jeg lykønske min søster.
• Når alle er kommet, skal vi nok skåle, og bagefter vil jeg lykønske min søster.

These are just stylistic variations. The original sentence is perfectly idiomatic.