Learn Hardcore Icelandic: Forvitin stelpa spyr ferðamanninn um veðrið á eyjunni. - A curious girl asks the tourist about the weather on the island.

If you want “the curious girl”, you normally make the noun definite:
hin forvitna stelpa or sú forvitna stelpa (more formal/literary), or you rely on context to make it clear you’re talking about a specific girl.

Why is the adjective forvitin placed before stelpa?

In Icelandic, as in English, adjectives usually come before the noun they modify:

forvitin stelpa – a curious girl
ungur maður – a young man
gott veður – good weather

Adjectives can come after the noun in some special constructions (e.g. with certain verbs: stelpan er forvitin – the girl is curious), but in a normal noun phrase like this, the order is adjective + noun.

Why is it forvitin stelpa and not forvitinn stelpa or forvitna stelpa?

Adjectives agree with the noun’s gender, number, and case.

stelpa is feminine, singular, nominative (subject of the sentence).
The adjective forvitinn (“curious”) has different forms; the feminine nominative singular form is forvitin.

So:

forvitinn maður – a curious man (maður = masculine)
forvitin stelpa – a curious girl (stelpa = feminine)
forvitin börn – curious children (different form again)

forvitna would be another case/form (e.g. a weak declension form or plural feminine), not correct here.

What exactly is spyr, and why that form of the verb?

spyr is the 3rd person singular present tense of the verb að spyrja – to ask.

Present tense of spyrja:

ég spyr – I ask
þú spyrð – you ask
hann/hún/það spyr – he/she/it asks
við spyrjum – we ask
þið spyrjið – you (pl) ask
þeir/þær/þau spyrja – they ask

The subject here is forvitin stelpa (“a curious girl”), which is 3rd person singular, so the correct form is spyr.

Why is ferðamanninn used instead of the dictionary form ferðamaður?

The dictionary form ferðamaður is nominative singular (“a traveler / tourist” as subject).

In this sentence, ferðamanninn is the object of ask (“asks the tourist”), so it must be in the accusative case and also definite (“the tourist”).

Declension (singular, masculine):

Nominative: ferðamaður – a tourist (subject)
Accusative: ferðamann – a tourist (object)
Dative: ferðamanni
Genitive: ferðamanns

With the definite article -inn:

Nominative definite: ferðamaðurinn – the tourist (subject)
Accusative definite: ferðamanninn – the tourist (object)

So ferðamanninn = “the tourist” in accusative case.

Why does -maður change to -mann- in ferðamanninn?

Nouns ending in -maður (“man, person”) often change to -mann- in the oblique cases (accusative, dative, genitive).

For ferðamaður:

Nom.: ferðamaður
Acc.: ferðamann
Dat.: ferðamanni
Gen.: ferðamanns

With the definite article, you attach -inn / -inum / -sins to that -mann- stem:

Acc. definite: ferðamanninn

This stem-change is a common pattern: nemandi → nemanda-, maður → mann-, etc.

What case is ferðamanninn, and why is that case used here?

Ferðamanninn is accusative singular definite.

The verb að spyrja (“to ask”) takes a direct object in the accusative case – the person being asked:

Hún spyr kennara. – She asks (a/the) teacher.
Hann spyr móður sína. – He asks his mother.
Forvitin stelpa spyr ferðamanninn. – A curious girl asks the tourist.

So, because the tourist is being asked (object), the noun is accusative: ferðamanninn.

What does the preposition um do in um veðrið, and why is veðrið in that form?

The preposition um usually means “about” or “around” and it goes with the accusative case.

um
- accusative

The noun veður (weather, neuter) in accusative definite form is veðrið (the weather).

So:

um veður – about (some) weather
um veðrið – about the weather

In this sentence, she is asking about the weather, so we get um veðrið.

Why is it á eyjunni and not á eyjuna?

The preposition á (“on, at, to”) can take accusative or dative, depending on meaning:

á + accusative – movement onto / to a place
- Hún fer á eyjuna. – She goes to the island.
á + dative – location on/in a place (no movement)
- Hún er á eyjunni. – She is on the island.

In spyr … um veðrið á eyjunni, the weather is located on the island (no movement), so á takes the dative, and we get eyjunni (dative definite), not eyjuna (accusative).

What exact form is eyjunni, and how is it built from eyja?

Dictionary form: eyja – island (feminine, nominative singular).

Singular declension (indefinite):

Nom.: eyja – an island
Acc.: eyju
Dat.: eyju
Gen.: eyju

With the definite article added (feminine, dative sing. ending -nni):

Dative definite: eyjunni – on the island / to the island (depending on preposition).

So in á eyjunni, eyjunni = dative singular definite of eyja (“the island”).

Could the word order be changed, like putting um veðrið á eyjunni earlier in the sentence?

Icelandic main clauses are generally verb-second (V2):

Some element (often the subject)
The finite verb
Rest of the sentence

Your sentence follows that:

Forvitin stelpa – curious girl (subject)
spyr – asks (finite verb)
ferðamanninn um veðrið á eyjunni – the rest

You can move other parts around after the verb for emphasis, for example:

Forvitin stelpa spyr um veðrið á eyjunni ferðamanninn.
(grammatically possible but sounds awkward; normal order keeps ferðamanninn directly after the verb)

What you cannot do in a neutral main clause is move something in front of the verb without moving the verb into the second position. For example:

Um veðrið á eyjunni spyr forvitin stelpa ferðamanninn.
– Here “Um veðrið á eyjunni” is first, the verb spyr is second. This is possible but has a strong emphasis on “about the weather on the island” and sounds more marked or stylistic.

How would the sentence change if the tourist were the one asking the girl?

You’d have to switch subject and object, and thus their cases:

Original:

Forvitin stelpa spyr ferðamanninn um veðrið á eyjunni.
– A curious girl (nom.) asks the tourist (acc.) about the weather on the island.

Reversed roles:

Forvitinn ferðamaður spyr stelpuna um veðrið á eyjunni.
– A curious tourist asks the girl about the weather on the island.

Changes:

ferðamaður becomes subject: forvitinn ferðamaður (masc. nom. sg.)
stelpa becomes object: stelpuna (fem. acc. sg. definite “the girl”)
Adjective agreement changes: forvitin stelpa vs forvitinn ferðamaður (feminine vs masculine).

How would I say “the curious girl asks the tourist” more explicitly?

You can mark both nouns as definite:

Hin forvitna stelpa spyr ferðamanninn.
– The curious girl asks the tourist.

Notes:

hin forvitna stelpa (or sú forvitna stelpa) both mean “the curious girl”; hin/sú are definite determiners.
ferðamanninn already has the definite ending -inn, so it means “the tourist”.