Ég vona að fræin fari að spíra áður en mánuðurinn er búinn.

Because this clause comes after Ég vona að ... (I hope that ...), Icelandic often uses the subjunctive to express hope, uncertainty, or something not yet realized.

• fer = present indicative of fara
• fari = present subjunctive of fara

So:

• Ég vona að fræin fari að spíra = I hope the seeds start sprouting

This is a very common pattern in Icelandic:

• Ég vona að hann komi. = I hope he comes.
• Ég vona að það verði gott veður. = I hope the weather will be good.

They do two different jobs.

1. að after vona

   • This means that
   • Ég vona að ... = I hope that ...

2. að after fari

   • This is part of the expression fara að + infinitive
   • fara að spíra = to start sprouting / to begin to sprout

So the sentence contains:

• one að as a conjunction
• one að as part of a verb pattern

They look the same, but they are not doing the same thing.

Literally, fara að spíra is something like go to sprout, but in real Icelandic it means start sprouting or begin to sprout.

This is a very common Icelandic structure:

• fara að rigna = start raining
• fara að sofa = go to sleep / start going to sleep
• fara að hlæja = start laughing

So yes, it is completely idiomatic and natural.

Because spíra is the infinitive after fara að.

In Icelandic, when one verb is followed by another in a pattern like fara að, the second verb is usually in the infinitive:

• fara að borða = start eating
• fara að lesa = start reading
• fara að spíra = start sprouting

So spíra is not conjugated here because fari is already the finite verb.

Fræin means the seeds.

It comes from:

• fræ = seed
• fræin = the seeds

A few useful points:

• fræ is a neuter noun
• here fræin is definite plural
• in this sentence it is the subject of the clause, so it is in the nominative

So in:

• að fræin fari að spíra

  the seeds are the ones doing the action of sprouting.

This is a good question, because some Icelandic neuter nouns can look the same in singular and plural in their basic indefinite form.

With fræ:

• fræ can mean a seed
• fræ can also mean seeds, depending on context

The definite form helps make things clearer:

• fræið = the seed
• fræin = the seeds

So fræin is definitely plural definite here.

Áður en means before when it introduces a whole clause.

So:

• áður en mánuðurinn er búinn = before the month is over

This is different from English, where before works on its own. In Icelandic, the common pattern is:

• áður en + clause

Examples:

• áður en ég fer = before I go
• áður en veturinn kemur = before the winter comes
• áður en mánuðurinn er búinn = before the month is over

So en is simply part of the normal conjunction here.

Literally, it means the month is finished.

More natural English would be:

• the month is over
• the month has ended

So:

• áður en mánuðurinn er búinn = before the month is over

This is a very common Icelandic way to talk about something being finished.

Because búinn agrees with mánuðurinn.

• mánuðurinn is masculine singular nominative
• therefore the adjective/past-participle form is búinn

Compare:

• dagurinn er búinn = the day is over
• vikan er búin = the week is over
• árið er búið = the year is over

So the ending changes to match the gender and number of the noun.

It is related, but the meaning is a little different.

1. X er búinn

   • means X is finished / over
   • mánuðurinn er búinn = the month is over

2. vera búinn að + infinitive

   • means to have already done something / be done doing something
   • Ég er búinn að lesa bókina. = I have finished reading the book.

So the word búinn is the same basic form, but the construction is different.

Because after áður en, you have a subordinate clause, and subordinate clauses usually keep normal subject + verb order in Icelandic.

So:

• áður en mánuðurinn er búinn = conjunction + subject + verb

This is normal and expected. Icelandic main clauses often show verb-second word order, but subordinate clauses are usually more straightforward.

Yes. You could say:

• Ég vona að fræin byrji að spíra áður en mánuðurinn er búinn.

That also means I hope the seeds start sprouting before the month is over.

The difference is small:

• fara að is extremely common for start to
• byrja að is also common and very clear

In many contexts, either one would sound natural.

It has three parts:

1. Ég vona

   • I hope

2. að fræin fari að spíra

   • that the seeds start sprouting

3. áður en mánuðurinn er búinn

   • before the month is over

So the whole sentence is:

• main clause: Ég vona
• content clause after að
• time clause after áður en

That makes the sentence a good example of how Icelandic links clauses together.