Motivacijsko pismo je spremno.

Because they both agree with pismo, which is a neuter singular noun.

In Croatian, adjectives must agree with the noun they describe in:

• gender
• number
• case

Here:

• pismo = neuter singular
• motivacijsko = neuter singular
• spremno = neuter singular

So the -o ending is the expected neuter singular form.

In Croatian, many nouns ending in -o or -e are neuter.
Pismo is one of them.

So:

• pismo = a neuter noun
• because of that, any adjective connected to it must also be neuter:
  • motivacijsko pismo
  • pismo je spremno

A learner may want to compare:

• dobar student = masculine
• dobra knjiga = feminine
• dobro pismo = neuter

Je is the 3rd person singular present tense of the verb biti = to be.

So:

• je = is

This sentence has the structure:

Motivacijsko pismo + je + spremno
subject + verb to be + adjective

So grammatically it works just like:

• Pismo je dugo. = The letter is long.
• Auto je novo. = The car is new.

Normally, no.

In standard Croatian, the present tense of biti is usually expressed, so you say:

• Motivacijsko pismo je spremno.

Leaving out je would sound incomplete in normal standard usage.

Croatian is not like some languages where the present-tense to be can regularly be omitted.

It is part of the predicate.

There are two different adjective uses here:

1. motivacijsko directly describes pismo

   • motivacijsko pismo = a motivation letter / cover letter

2. spremno comes after je and says what the subject is like

   • pismo je spremno = the letter is ready

So spremno is a predicate adjective.

It is in the nominative singular because it is the subject of the sentence.

You can identify the subject by asking:

• What is ready?

Answer:

• Motivacijsko pismo

Since it is the subject, nominative is exactly what you would expect.

It matches the subject and is also in the nominative singular neuter.

With biti + adjective, Croatian usually uses a predicate adjective that agrees with the subject:

• Pismo je spremno.
• Knjiga je spremna.
• Student je spreman.

So:

• spreman = masculine singular
• spremna = feminine singular
• spremno = neuter singular

Croatian word order is flexible, but the normal, neutral order here is:

Motivacijsko pismo je spremno.

Other orders are possible, but they sound more marked and usually add emphasis or a special style.

For example:

• Spremno je motivacijsko pismo.
  This is possible, but it sounds less neutral and more stylistic or emphatic.

For learners, the safest choice is the standard neutral order:

• subject + je + adjective

Yes, it is a common expression.

Depending on context, motivacijsko pismo can refer to:

• a motivation letter
• a cover letter, especially for a job or application

So even if English sometimes prefers cover letter, Croatian often uses motivacijsko pismo in that role.

Because spreman is the masculine singular form.

The noun here is pismo, which is neuter, so the adjective must be spremno.

Compare:

• Student je spreman. = masculine
• Prijava je spremna. = feminine
• Pismo je spremno. = neuter

This kind of agreement is one of the most important patterns in Croatian grammar.

A simple learner-friendly pronunciation is:

mo-tee-va-CIY-sko PIS-mo ye SPREM-no

A few notes:

• j in Croatian sounds like English y in yes
• je sounds roughly like ye
• stress can vary by dialect and teaching style, but this approximation is good enough for a beginner

Letter-by-letter:

• Motivacijsko ≈ mo-ti-va-ciy-sko
• pismo ≈ pee-smo
• je ≈ ye
• spremno ≈ sprem-no

Yes, pismo can have more than one meaning depending on context.

Common meanings include:

• letter as a written message
• script or alphabetic writing system

In motivacijsko pismo, the context clearly shows it means a letter/document, not a writing system.