Við lagfærum númeraplötuna áður en aðalskoðunin byrjar.

Við means we.

lagfærum is the present tense of the verb lagfæra, meaning to repair, fix, or adjust. In this sentence, við lagfærum means we repair / we are fixing / we fix.

Icelandic present tense often covers meanings that in English could be:

• we fix
• we are fixing
• sometimes even we will fix, depending on context

Here it is simply the present form agreeing with við (we).

The base form is lagfæra.

This is the infinitive, equivalent to English to repair / to fix.

The form lagfærum is specifically the 1st person plural present tense form, used with við:

• ég lagfæri = I repair
• við lagfærum = we repair

Because it is:

• singular
• definite (the number plate)
• accusative case
• and the noun is feminine

The base noun is númeraplata = number plate / license plate.

In this sentence, it is the direct object of lagfærum, so it appears in the accusative:

• númeraplata = a number plate
• númeraplatan = the number plate (nominative)
• númeraplötuna = the number plate (accusative)

The vowel change from plata to plötu- is a normal inflection pattern in many Icelandic nouns.

Because Icelandic very commonly forms compound nouns by joining words together.

So:

• númera- relates to numbers
• plata means plate

Together, númeraplata means number plate / license plate.

This is very normal in Icelandic. Where English often uses two words, Icelandic often prefers one compound word.

áður en means before in the sense of before something happens.

It introduces a clause:

• áður en aðalskoðunin byrjar = before the main inspection starts

Think of it as:

• áður = earlier / before
• en = introducing the clause after it

So the pattern is:

• main clause + áður en + subordinate clause

Example from the sentence:

• Við lagfærum númeraplötuna = We fix the number plate
• áður en aðalskoðunin byrjar = before the main inspection starts

aðalskoðunin is the subject of the subordinate clause, so it is in the nominative case.

The base noun is aðalskoðun:

• aðal- = main, principal
• skoðun = inspection

So:

• aðalskoðun = a main inspection
• aðalskoðunin = the main inspection

The ending -in is the definite article attached to the noun, which is how Icelandic usually says the.

Because its subject, aðalskoðunin (the main inspection), is singular.

byrjar is the 3rd person singular present tense of byrja (to begin / to start).

So:

• aðalskoðunin byrjar = the main inspection starts

If the subject were plural, the verb form would change.

That is a very good question.

Icelandic is often verb-second (V2) in main clauses, but this sentence contains a subordinate clause after áður en.

Main clause:

• Við lagfærum númeraplötuna
  Here the finite verb lagfærum is in the expected main-clause position.

Subordinate clause:

• áður en aðalskoðunin byrjar
  Here the normal order is subject + verb:
• aðalskoðunin = subject
• byrjar = verb

So the sentence shows a common contrast:

• main clause: V2 behavior
• subordinate clause: more straightforward subject-verb order

Grammatically, both verbs are in the present tense:

• lagfærum
• byrjar

But in meaning, the sentence can easily refer to a future situation, especially if it is about a scheduled event:

• We’ll fix the number plate before the main inspection starts

This is very natural in Icelandic, just as English can also use present forms in time clauses:

• We’ll do it before the inspection starts

So even though the forms are present tense, the overall meaning may be future-oriented.

A fairly literal breakdown would be:

• Við = we
• lagfærum = repair/fix
• númeraplötuna = the number plate
• áður en = before
• aðalskoðunin = the main inspection
• byrjar = starts

So a literal translation would be:

We repair the number plate before the main inspection starts.

Depending on context, more natural English might be:

• We’ll fix the license plate before the main inspection starts.
• We are fixing the number plate before the main inspection starts.

A rough pronunciation guide for áður is something like OW-thur or OW-dhur, but not exactly either of those.

A few helpful points:

• á is like ow in now, but longer
• ð is like the th in this (a voiced sound), not the th in thin
• u here is pronounced like an Icelandic u, not exactly like English oo
• r is rolled or tapped, unlike most English r

So áður may be approximated for an English speaker as:

• OW-thur (very rough)

The important part is that ð is a soft voiced sound, not a hard d.

Often, yes, depending on context.

Both lagfæra and laga can mean to fix / repair, but there can be slight differences in tone or usage:

• laga is very common and broad: fix, repair, put right
• lagfæra can sound a bit more like repair, adjust, make good, sometimes slightly more formal or technical

So a sentence with laga could also make sense:

• Við lögum númeraplötuna áður en aðalskoðunin byrjar.

That said, the original sentence with lagfærum is perfectly natural.