Smekkurinn verður oft skítugur þegar hún borðar sjálf.

The ending -inn is the definite article attached to the noun.

So:

• smekkur = bib
• smekkurinn = the bib

Icelandic usually puts the at the end of the noun instead of using a separate word like English does.

Also, smekkurinn is the subject of the sentence, so it is in the nominative singular.

Icelandic handles articles differently from English:

• the is usually added to the end of the noun
• there is no true indefinite article corresponding exactly to English a/an

So:

• smekkur can mean a bib or just bib, depending on context
• smekkurinn means the bib

This is very common in Icelandic and is something English speakers have to get used to.

Because verða means become / get, not simply be.

So:

• Smekkurinn er skítugur = The bib is dirty
• Smekkurinn verður skítugur = The bib gets dirty / becomes dirty

In this sentence, the idea is that the bib ends up dirty as a result of the eating, so verður is the natural choice.

Also, even though verður can sometimes look like will become, here it is just present tense with a habitual meaning because of oft:

• verður oft skítugur = often gets dirty

Because Icelandic adjectives agree with the noun they describe in gender, number, and case.

Here, smekkurinn is:

• masculine
• singular
• nominative

So the adjective must also be masculine singular nominative:

• skítugur

Compare:

• masculine: skítugur
• feminine: skítug
• neuter: skítugt

So if the noun were a different gender, the adjective form would change too.

Here sjálf means something like:

• herself
• on her own
• by herself

It adds emphasis to hún and suggests that she is eating without help or independently.

So hún borðar sjálf is not just she eats, but more like:

• she eats by herself
• she feeds herself

The exact best English wording depends on context, but the core idea is that she herself is doing the eating.

Because sjálfur also agrees with the person it refers to.

Here it refers to hún (she), which is:

• feminine
• singular
• nominative

So the correct form is sjálf.

Compare:

• hann borðar sjálfur = he eats by himself
• hún borðar sjálf = she eats by herself
• barnið borðar sjálft = the child eats by itself / on its own

This agreement is very important in Icelandic.

Because this is an emphatic use of sjálfur, not an object pronoun.

English uses herself in two different ways:

1. reflexive: She sees herself
2. emphatic/intensive: She herself did it or She ate by herself

In Icelandic, those are handled differently.

In this sentence, sjálf is emphasizing the subject hún, so it means she herself / on her own.

If you needed a true reflexive object, Icelandic would usually use sig:

• Hún sér sig = She sees herself

So hún borðar sjálf is not about her eating herself as an object; it means she is eating independently.

Þegar means when.

It introduces a subordinate clause:

• þegar hún borðar sjálf = when she eats by herself

So the whole sentence has:

• main clause: Smekkurinn verður oft skítugur
• subordinate clause: þegar hún borðar sjálf

This is very similar to English in meaning, even though Icelandic word order works a bit differently in general.

After a subordinating word like þegar, Icelandic normally uses regular subordinate clause word order.

So:

• þegar hún borðar sjálf

has:

• þegar = when
• hún = subject
• borðar = verb
• sjálf = emphatic word referring to the subject

English speakers often learn early that Icelandic is a verb-second language, but that rule mainly applies to main clauses. In subordinate clauses like this one, the verb does not have to come second in the same way.

So this word order is completely normal.

Oft means often, and in a neutral sentence it commonly comes after the finite verb:

• verður oft skítugur

This is a very natural placement for frequency adverbs in Icelandic.

So the structure is roughly:

• Smekkurinn = subject
• verður = finite verb
• oft = adverb
• skítugur = adjective/complement

You may see adverbs moved around for emphasis, but this placement is standard and common.

Usually skítugur means dirty, grubby, or messy. It does not have to mean extremely filthy.

In this sentence, it most naturally suggests that the bib gets food on it and becomes messy during eating.

So it is a very natural word here, and it does not necessarily imply anything dramatic.