Krónan er ekki eins sterk og í fyrra.

Because -n is the suffixed definite article in Icelandic.

• króna = a krona / krona
• krónan = the krona

Icelandic often attaches the to the end of the noun instead of using a separate word the way English does.

Er is the 3rd person singular present form of vera, which means to be.

So:

• ég er = I am
• þú ert = you are
• hann/hún/það er = he/she/it is

Since krónan is singular, the sentence uses er: Krónan er ... = The krona is ...

In a normal Icelandic main clause, the negation ekki usually comes after the finite verb.

So the pattern is:

• Krónan er sterk = The krona is strong
• Krónan er ekki sterk = The krona is not strong

That placement is very typical in Icelandic word order.

This is the Icelandic way to say not as strong as.

The pattern is:

• eins ... og ... = as ... as ...
• ekki eins ... og ... = not as ... as ...

So:

• eins sterk og = as strong as
• ekki eins sterk og = not as strong as

This is a very useful pattern to memorize because it works with many adjectives:

• ekki eins stór og = not as big as
• ekki eins fljótur og = not as fast as
• ekki eins dýr og = not as expensive as

Because in the structure eins ... og ..., Icelandic uses og where English uses the second as.

So:

• eins sterk og í fyrra = as strong as last year

This can feel strange because og usually means and, but in this comparison pattern it functions as part of as ... as.

By contrast, en is commonly used with a comparative form:

• sterkari en ... = stronger than ...
• veikari en ... = weaker than ...

So Icelandic distinguishes:

• eins sterk og = as strong as
• sterkari en = stronger than

Because adjectives in Icelandic agree with the noun they describe in gender, number, and case.

Króna is a feminine singular noun, so the adjective must match it:

• masculine: sterkur
• feminine: sterk
• neuter: sterkt

Since krónan is feminine singular, the correct form is sterk.

Because Icelandic predicate adjectives also agree with the subject.

In English, adjectives do not change form:

• the man is strong
• the woman is strong
• the house is strong

But in Icelandic they do change:

• Maðurinn er sterkur
• Konan er sterk
• Húsið er sterkt

So in Krónan er ekki eins sterk og í fyrra, sterk agrees with krónan even though it comes after the verb.

Í fyrra is a fixed expression meaning last year.

You should learn it as a set phrase. Even though í often means in, the whole expression í fyrra functions adverbially and means last year.

Examples:

• Ég var á Íslandi í fyrra. = I was in Iceland last year.
• Það var kaldara í fyrra. = It was colder last year.

Because í fyrra is already a complete time expression. Icelandic does not need to add a separate noun like ári here.

So the sentence does not mean something incomplete like in previous...; í fyrra is simply the normal idiomatic way to say last year.

Yes. A comparative version would also be possible, for example:

• Krónan er veikari en í fyrra. = The krona is weaker than last year.

But ekki eins sterk og í fyrra and veikari en í fyrra are not exactly the same in tone:

• ekki eins sterk og ... = not as strong as ...
• veikari en ... = weaker than ...

The original sentence uses the not as ... as ... structure rather than the direct comparative. Both are natural, but the grammar is different.