Úrbótaáætlunin er tilbúin.

Because Icelandic makes very frequent use of compounds, and they are normally written as a single word.

Here, úrbótaáætlunin can be broken down like this:

• úrbóta-
• áætlun
• -in

The main noun is áætlun (plan), and everything before it modifies it. A useful rule in Icelandic compounds is that the last part is the head: this word is a kind of áætlun, not a kind of úrbót.

The dictionary form without the definite article is úrbótaáætlun.

Because Icelandic very often puts the definite article onto the end of the noun instead of using a separate word.

So:

• úrbótaáætlun = improvement plan / action plan
• úrbótaáætlunin = the improvement plan / the action plan

The ending -in here is the definite article attached to a feminine singular noun in the nominative.

This is a very common thing in Icelandic compounds: the first element often appears in a genitive or linking form rather than in its plain dictionary form.

Here, úrbóta- comes from úrbót and means something like of improvements / of remedies / corrective in the compound.

So the compound is built in a way that is roughly like:

• úrbótaáætlun = plan of improvements / remedial plan / corrective action plan

You do not always need to translate that internal structure literally, but it helps explain why the form is úrbóta-.

Er is the present tense form of vera, the Icelandic verb to be.

In this sentence it means is:

• Úrbótaáætlunin er tilbúin.
• The improvement plan is ready.

It is er because the subject is third person singular:

• hún er = she/it is
• áætlunin er = the plan is

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

The noun áætlun is:

• feminine
• singular
• here, nominative

So the adjective must match that:

• masculine: tilbúinn
• feminine: tilbúin
• neuter: tilbúið

Since úrbótaáætlunin is feminine singular, the correct form is tilbúin.

In this sentence, it functions as an adjective meaning ready or prepared.

The actual verb in the sentence is er. So the structure is:

• subject
  • verb
    • predicate adjective

That means:

• Úrbótaáætlunin = subject
• er = verb
• tilbúin = adjective describing the subject

Historically, tilbúinn / tilbúin / tilbúið is related to the verb tilbúa (to prepare), but in sentences like this learners should usually treat it as an adjective.

The subject úrbótaáætlunin is in the nominative case.

After vera (to be), predicate adjectives are also usually in the nominative, so tilbúin is nominative as well.

So the sentence is basically:

• Úrbótaáætlunin — nominative feminine singular
• er
• tilbúin — nominative feminine singular to agree with the subject

This is one reason Icelandic learners need to pay attention not just to meaning, but also to agreement.

Because this is the normal pattern with vera (to be) and a predicate adjective.

The structure is:

• noun + er + adjective

So:

• Húsið er stórt. = The house is big.
• Bókin er góð. = The book is good.
• Úrbótaáætlunin er tilbúin. = The improvement plan is ready.

This works very much like English X is ready / X is big / X is good.

A rough English-friendly approximation is:

OOR-boh-ta-OW-eye-tluh-nin er TIL-boo-in

A few useful notes:

• Stress in Icelandic is usually on the first syllable of each word.
• So you stress ÚR in úrbótaáætlunin and TIL in tilbúin.
• The accent marks in ú, á, and æ do not mainly mark stress; they mark vowel quality.

Very roughly:

• úrbótaáætlunin ≈ OOR-boh-ta-OW-eye-tluh-nin
• er ≈ ehr
• tilbúin ≈ TIL-boo-in

That said, Icelandic pronunciation has details that English spelling cannot show very well, so audio from a native speaker or dictionary is especially helpful here.