Ef við endurnýtum það sem er í góðu lagi, þurfum við ekki alltaf að kaupa nýtt.

Because Icelandic normally follows a verb-second pattern in main clauses.

Here, the whole Ef... clause comes first:

Ef við endurnýtum það sem er í góðu lagi, ...

That first clause takes the first position, so in the main clause the finite verb must come next:

þurfum við ekki alltaf að kaupa nýtt

So the order is:

1. Ef-clause
2. þurfum (finite verb)
3. við (subject)

If you put the main clause first, you would get the more familiar order:

Við þurfum ekki alltaf að kaupa nýtt ef við endurnýtum það sem er í góðu lagi.

það sem is a very common Icelandic way to mean what or that which.

So:

það sem er í góðu lagi
= what is in good condition
= that which is okay

Even though það by itself often means it or that, in this structure það sem works together as a relative expression.

You will see this a lot in Icelandic:

• Ég borða það sem ég vil. = I eat what I want.
• Taktu það sem þú þarft. = Take what you need.

endurnýtum is the 1st person plural present tense of endurnýta.

So:

• ég endurnýti = I reuse
• þú endurnýtir = you reuse
• við endurnýtum = we reuse

In this sentence:

við endurnýtum = we reuse

The ending -um is a very common ending for we in the present tense.

It most naturally means reuse or use again.

In this sentence, reuse is the best fit, because the idea is:

If we reuse what is still in good condition, we do not always need to buy new things.

A useful distinction is:

• endurnýta = reuse / use again
• endurvinna = recycle

Sometimes English uses recycle loosely, but Icelandic often keeps these ideas more separate.

í góðu lagi is a fixed expression meaning:

• okay
• all right
• in good condition

In this sentence, in good condition is the best interpretation.

Literally, it is something like in good order/condition.

Why góðu lagi? Because í often takes the dative when it describes a state or location rather than movement. So the phrase appears in the dative:

• í góðu lagi

This is a very common expression, so it is worth learning as a chunk.

Because the noun is left unstated.

að kaupa nýtt literally means something like:

• to buy something new
• to buy a new one
• to buy new things

Icelandic often uses a neuter singular adjective on its own in a general sense like this. So nýtt does not necessarily mean one specific neuter noun is missing; it is more of a broad, generic new stuff / something new idea.

If you wanted to name the noun explicitly, you could say something like:

• að kaupa nýja hluti = to buy new things

But að kaupa nýtt sounds natural and idiomatic.

Because þurfa is followed by an infinitive, usually with að.

So:

• þurfa að gera = need to do
• þurfum að kaupa = we need to buy

In the sentence:

þurfum við ekki alltaf að kaupa nýtt
= do we not always need to buy new things

This is similar to English need to buy, except Icelandic uses the infinitive marker að.

No. ekki alltaf means not always, not never.

So the sentence means:

• sometimes we do need to buy new things
• but not every time

Compare:

• ekki alltaf = not always
• aldrei = never

So this sentence is making a moderate claim, not an absolute one.

Because the sentence begins with a subordinate clause:

Ef við endurnýtum það sem er í góðu lagi, ...

Then the main clause follows:

þurfum við ekki alltaf að kaupa nýtt.

In Icelandic, it is normal to separate an opening subordinate clause from the main clause with a comma. So the comma helps show the structure:

• If we reuse what is in good condition,
• we do not always need to buy new.

You could say:

Við þurfum ekki alltaf að kaupa nýtt ef við endurnýtum það sem er í góðu lagi.

That means the same thing.

The difference is mostly word order:

• With the if-clause first, you get þurfum við because of verb-second order.
• With the main clause first, you get the more straightforward við þurfum.

Both are natural.

These two letters are very important in Icelandic.

• þ is like the th in think
• ð is like the th in this

So:

• það sounds roughly like thath with the voiced th at the end
• þurfum begins with the unvoiced th sound from think

A rough guide:

• það ≈ thadh
• þurfum ≈ THUR-vum or THUR-fum depending on how carefully you want to approximate it

The exact Icelandic sounds are not identical to English ones, but those comparisons are a good start.

Yes.

The whole part það sem er í góðu lagi contains a relative clause:

• það sem = what / that which
• er í góðu lagi = is in good condition

So the structure is:

endurnýtum [það sem er í góðu lagi]

That entire bracketed part is the object of endurnýtum.

In other words, we are reusing the things that are still okay.