Learn Hardcore Icelandic: Í framtíðinni mun hún hafa lært fleiri hljóðfæri ef hún æfir daglega. - In the future she will have learned more instruments if she practices daily.

The finite verb (here: mun) normally comes in second position in the sentence, regardless of what comes first.
If you put an adverbial like Í framtíðinni at the beginning, the finite verb must still come second, so the subject moves after the verb.

So:

Í framtíðinni mun hún hafa lært…
1st: Í framtíðinni (adverbial)
2nd: mun (finite verb)
3rd: hún (subject)

You could also say:

Hún mun í framtíðinni hafa lært fleiri hljóðfæri…

Here the subject hún is first, so mun is still second.

What exactly does mun hafa lært mean, and why do we use that instead of just mun læra?

Mun hafa lært is the future perfect (or “future of the perfect”):

mun = future auxiliary (will)
hafa = have
lært = past participle of læra (to learn)

Together: mun hafa lært ≈ “will have learned”.

Use mun hafa lært when you want to say that, at some point in the future, the action will already be completed.
Use mun læra (will learn) when you just talk about a future action, not its completion relative to a later point.

Examples:

Í framtíðinni mun hún læra fleiri hljóðfæri.
In the future she will learn more instruments (at some time, generally).
Í framtíðinni mun hún hafa lært fleiri hljóðfæri.
In the future she will have learned more instruments (by that time, the learning is already done).

What grammatical role and form does lært have here?

Lært is the supine / past participle form of the verb læra (to learn).

With hafa (to have), this form makes the perfect or pluperfect, and with mun hafa it forms the future perfect:

Ég hef lært. – I have learned.
Ég hafði lært. – I had learned.
Ég mun hafa lært. – I will have learned.

So in mun hún hafa lært, lært is not a finite verb; it is part of the verb phrase that depends on hafa and ultimately on mun.

Why is it Í framtíðinni and not something like í framtíð? What is the ending -inni?

Í framtíðinni literally means “in the future (the)”, using:

í = preposition in
framtíð = future (a feminine noun)
-inni = dative singular definite ending for many feminine nouns

Key points:

The preposition í here takes the dative case, because we’re talking about a location in time, not movement into.
Framtíð is feminine; its dative singular is framtíð
- inni → framtíðinni.
The definite article in Icelandic is usually attached to the noun instead of being a separate word like “the”.

So:

framtíð = a future / future (indefinite)
framtíðinni = the future (in the dative case)
í framtíðinni = in the future

What case is framtíðinni in, and why does í require that case here?

Framtíðinni is in the dative singular definite.

The preposition í can take either accusative (for motion into) or dative (for position in / within). In expressions of time, when you mean “during / in” a period, í usually takes the dative:

Í framtíðinni – in the future (dative)
Í fortíðinni – in the past (dative)
Í vikunni – in the week / this week (dative)

So í + dative here expresses a stable location in time, not movement.

What does fleiri mean exactly, and how is it different from meira?

Both fleiri and meira can be translated as more, but they are used differently:

Fleiri = more countable items, used with plural nouns.
It is the comparative of margir (many).
- fleiri hljóðfæri – more instruments
- fleiri bækur – more books
Meira = more of an uncountable quantity (or abstract amount).
It is the comparative of mikill (much, a lot).
- meira vatn – more water
- meira tónlist – more music
- meira tíma – more time

In the sentence, hljóðfæri (instruments) are countable, so fleiri hljóðfæri is correct, not meira hljóðfæri.

Why does hljóðfæri look the same in singular and plural here?

Hljóðfæri is a neuter noun that has the same form in nominative and accusative, singular and plural:

eitt hljóðfæri – one instrument
tvö hljóðfæri – two instruments
ég spila á hljóðfæri – I play an instrument / instruments (context decides)
fleiri hljóðfæri – more instruments

So in fleiri hljóðfæri, the noun hljóðfæri does not change its form to show plural; the word fleiri tells you it’s plural.

Why is it ef hún æfir daglega and not ef hún mun æfa daglega?

In Icelandic, after ef (if) introducing a real condition about the future, you normally use the present tense, not a future auxiliary:

ef hún æfir daglega – if she practices daily
(literally “if she practices daily”, present tense, but understood as future)

Using mun in the ef‑clause (ef hún mun æfa) is unusual and typically unnecessary or stylistically odd. It can appear in some emphatic or special contexts, but the default and most natural form for future conditions is present tense in the ef‑clause.

Why is the present tense æfir used for something that happens in the future?

Icelandic often uses the present tense to talk about the future, especially when the future time is clear from context or from other parts of the sentence.

In this sentence, the “future” meaning is already established by:

Í framtíðinni – in the future
mun hún hafa lært – she will have learned

So ef hún æfir daglega is formally in the present, but understood as “if she practices (in the future) on a daily basis”. This is similar to English:
“If she practices every day, she will have learned more instruments.”
(we also use present in the if‑clause in English).

What does daglega mean, and how is it formed?

Daglega means daily, every day, on a daily basis.

It is an adverb derived from dagur (day). A common pattern is:

noun dagur → stem dag-
add -lega to form an adverb: daglega

So:

hún æfir daglega – she practices daily
You can often paraphrase it as á hverjum degi – on every day / every day

Both daglega and á hverjum degi are natural; daglega is simply more compact.

Could the word order be different, for example Hún mun hafa lært fleiri hljóðfæri í framtíðinni ef hún æfir daglega? Is that still correct?

Yes, that word order is also grammatical:

Hún mun hafa lært fleiri hljóðfæri í framtíðinni ef hún æfir daglega.

Key points:

In main clauses, the finite verb (mun) must be in second position.
Here, Hún is first, mun is second → correct.
Adverbials like í framtíðinni, daglega, etc. can move around quite freely, as long as they don’t break the V2 rule.

Different word orders can change emphasis or style slightly, but they’re often both acceptable.
The original sentence Í framtíðinni mun hún hafa lært… puts more emphasis on “in the future” by placing it first.

Why is there no comma before ef in this Icelandic sentence?

Modern Icelandic comma rules are not identical to English ones:

A comma is not automatically required before every ef‑clause (if‑clause).
You usually don’t put a comma before a short ef‑clause that flows naturally with the main clause.

So:

Í framtíðinni mun hún hafa lært fleiri hljóðfæri ef hún æfir daglega.
is perfectly standard without a comma.

You might sometimes see a comma for clarity in very long or complex sentences, but here it’s not needed and is typically omitted.