Når alt kommer til alt, mangler flatpakken en treplugg.

It is an idiomatic expression meaning when all is said and done, in the end, or ultimately.

Word for word, it looks like:

• når = when
• alt = everything
• kommer = comes
• til alt = to everything

But you should learn the whole phrase as a fixed expression, because the literal breakdown is less useful than the idiomatic meaning.

Because Norwegian follows the V2 rule in main clauses: the finite verb usually comes in the second position.

Here, the sentence begins with the adverbial phrase Når alt kommer til alt. After that fronted phrase, the verb must come next:

• Når alt kommer til alt, mangler flatpakken en treplugg.

If you started directly with the subject, you would get:

• Flatpakken mangler en treplugg.

Both are fine, but once the opening phrase is moved to the front, mangler has to come before flatpakken.

Because mangle means to lack, to be missing, or not have something that should be there.

So:

• Flatpakken mangler en treplugg = The flat-pack is missing a wooden dowel / The flat-pack lacks a wooden dowel

This is different from emotionally missing someone, where Norwegian would often use savne:

• Jeg savner deg = I miss you

So mangle is the correct verb for missing parts or absent items.

Flatpakken is the definite singular form of flatpakke, meaning the flat-pack or the flat-pack package.

Breakdown:

• flatpakke = flat-pack
• flatpakken = the flat-pack

The ending -en marks the definite form here.

Because the sentence refers to a specific flat-pack, not just any flat-pack.

Compare:

• en flatpakke = a flat-pack
• flatpakken = the flat-pack

So the sentence is talking about a particular package, probably one already known from the context.

Treplugg is a compound noun:

• tre = wood
• plugg = plug, peg, dowel

So treplugg means wooden dowel or wooden peg.

Norwegian very often combines nouns into one word where English may use two words or an adjective + noun combination. So writing it as one word is completely normal.

Because treplugg is a singular countable noun, and here it is indefinite:

• en treplugg = a wooden dowel

That means the flat-pack is missing one wooden dowel, not a specific previously mentioned one.

If it were definite, it would be:

• trepluggen = the wooden dowel

Because mangle normally takes a direct object in Norwegian.

So you say:

• mangle noe = to lack something

Examples:

• Jeg mangler tid. = I lack time.
• Vi mangler sukker. = We are missing sugar.
• Flatpakken mangler en treplugg. = The flat-pack is missing a wooden dowel.

You do not need a preposition like på or med here.

Yes. In this sentence, flatpakken is the grammatical subject.

• flatpakken = subject
• mangler = verb
• en treplugg = direct object

So the structure is basically:

• The flat-pack lacks a wooden dowel

Norwegian often expresses this kind of idea with the thing that is incomplete as the subject.

Yes, that is also a natural sentence.

It means something like:

• There is a wooden dowel missing from the flat-pack

This version focuses a bit more on the missing item itself, while:

• Flatpakken mangler en treplugg

focuses on the flat-pack as incomplete.

Both are good Norwegian.

It is a normal idiomatic expression and is still used in modern Norwegian. It can appear in both speech and writing.

It may sound slightly thoughtful or reflective, like when all is said and done in English, but it is not strange or outdated.

Yes. Depending on style, you could translate it as:

• When all is said and done, the flat-pack is missing a wooden dowel.
• In the end, the flat-pack lacks a wooden dowel.
• Ultimately, the flat-pack is missing one wooden peg.

The exact English wording can vary, but the Norwegian grammar stays the same.