Saumakonan sagði að faldurinn á pilsinu væri of langur.

Those endings are the suffixed definite article in Icelandic. Instead of using a separate word like English the, Icelandic usually attaches definiteness to the noun itself.

In this sentence:

• saumakonan = the seamstress
• faldurinn = the hem
• pilsinu = the skirt in the form required after á

The exact article ending changes depending on the noun’s gender, number, and case.

The dictionary forms are:

• saumakona = seamstress
• segja = to say
• faldur = hem
• pils = skirt
• vera = to be
• langur = long
• of = too, excessively

So the sentence uses inflected forms of these basic words:

• saumakonan ← saumakona
• sagði ← segja
• faldurinn ← faldur
• pilsinu ← pils
• væri ← vera
• langur ← langur

Because á can govern the dative when it means location or position, roughly on or on/in relation to something static.

Here, the hem is understood as being on the skirt, so Icelandic uses:

• á pilsinu = on the skirt

Since pils is a neuter noun, its dative singular definite form is pilsinu.

A helpful contrast:

• á pilsinu = on the skirt, located on it
• if motion onto something were involved, á could take the accusative instead

In this sentence, there is no motion, only description, so dative is used.

Because Icelandic often uses á + dative for a part or feature that is physically on something.

So:

• faldurinn á pilsinu literally means something like the hem on the skirt

That is a very natural way to say the hem of the skirt in Icelandic.

A genitive-style expression may sometimes be possible in other contexts, but here á pilsinu is the most natural everyday phrasing.

It is part of the noun phrase.

The structure is:

• faldurinn á pilsinu = the hem on the skirt

So á pilsinu modifies faldurinn, not sagði and not really væri.

That matters because the sentence is not saying the act of saying happened on the skirt. It is identifying which hem is being talked about: the one belonging to / on the skirt.

Because this is an indirect speech clause after sagði að.

In Icelandic, when you report what someone said, thought, claimed, etc., the subordinate clause often uses the subjunctive, especially in careful standard language. That is what væri is here: the past subjunctive of vera.

So:

• Saumakonan sagði að ... væri ... = The seamstress said that ... was ...

To an English speaker, this can feel strange, because English usually just uses was. Icelandic often marks reported speech more explicitly with the subjunctive.

Not really, even though væri can sometimes correspond to would be in other contexts.

Here, væri is best understood as the subjunctive form used in reported speech, so in normal English translation it often comes out simply as was.

So in this sentence:

• væri of langur is understood as was too long, not necessarily would be too long

The form is the same, but the function depends on context.

For a learner, the safest answer is: use væri in this sentence.

After sagði að, standard Icelandic very often prefers the subjunctive in indirect speech:

• Hún sagði að það væri rétt.

You may sometimes encounter the indicative in real-life speech or in contexts where the speaker presents the content more directly as fact, but væri is the expected and most teachable form here.

So if you are learning standard Icelandic, Saumakonan sagði að faldurinn á pilsinu væri of langur is the form to aim for.

Because the adjective agrees with faldurinn, and faldur is masculine singular nominative.

After vera, predicate adjectives agree with the subject in gender, number, and case.

Here:

• faldurinn = masculine singular nominative
• so the adjective must also be masculine singular nominative:
  • langur

Compare:

• faldurinn er langur = the hem is long
• saumakonan sagði að faldurinn ... væri langur = the seamstress said that the hem was long

It does not agree with pilsinu, because the hem is the thing being described, not the skirt.

Because of is just an adverb meaning too. It does not change the case or form of the adjective by itself.

The adjective still has to match the subject:

• faldurinn → masculine singular nominative
• therefore langur

So:

• of langur = too long

The reason it is not langan is that after vera, the adjective is a predicate adjective, and here that predicate stays in the nominative.

After the conjunction að meaning that, Icelandic does not use the normal main-clause V2 pattern.

So instead of putting the verb second the way a main clause often does, the subordinate clause typically has a more straightforward order:

• að faldurinn á pilsinu væri of langur

That is:

• að
  • subject + modifier + verb + adverb + adjective

A good practical point for learners is:

• in main clauses, Icelandic often has verb-second
• in að-clauses, that pattern disappears

That is why væri comes after the subject phrase here.

Of means too in the sense of excessively.

So:

• of langur = too long

This is a very common Icelandic word. It is used with adjectives and adverbs much like English too:

• of stór = too big
• of dýrt = too expensive
• of hratt = too fast

So in your sentence, the problem is not that the hem is merely long, but that it is longer than it should be.

Because the two verbs are doing different jobs.

• sagði is the main verb of the sentence, and it simply tells you that the act of speaking happened in the past.
• væri is inside a subordinate clause and shows the content of what was said.

In English, both often look like past forms:

• She said that the hem was too long

In Icelandic, the reported content is often put into the subjunctive rather than an ordinary past indicative. So the tense relationship is not expressed in exactly the same way as in English.

Að here is a conjunction meaning that.

It introduces the clause containing what the seamstress said:

• Saumakonan sagði = The seamstress said
• að faldurinn á pilsinu væri of langur = that the hem on the skirt was too long

Do not confuse this að with the infinitive marker að meaning to before a verb. Icelandic uses the same word for both functions, but here it is clearly a conjunction introducing a subordinate clause.