Razlog otkazivanja leta je tajna.

A word-for-word breakdown is:

• razlog = reason
• otkazivanja = of cancellation / of cancelling
• leta = of the flight
• je = is
• tajna = a secret

So the sentence literally looks like:

reason of-cancellation of-flight is secret

A natural English translation is The reason for the flight cancellation is a secret.

They are both in the genitive case.

Croatian often links nouns together this way:

• razlog nečega = reason for/of something
• otkazivanje nečega = cancellation of something

So here you get a chain:

• razlog otkazivanja = reason for the cancellation
• otkazivanja leta = cancellation of the flight

Put together:

• razlog otkazivanja leta = the reason for the flight cancellation

This kind of noun chain is very common in Croatian.

Otkazivanje is a verbal noun. It comes from the verb otkazati / otkazivati, meaning to cancel.

English often uses:

• a gerund: cancelling
• or a noun: cancellation

Croatian often uses a verbal noun ending like -anje, -enje, or -ivanje:

• putovati → putovanje = travelling / travel
• otkazati → otkazivanje = cancelling / cancellation

In this sentence, otkazivanja is the genitive singular form of otkazivanje.

The basic dictionary form is let = flight.

Here it changes to leta because it is in the genitive singular, after otkazivanje:

• let = flight
• otkazivanje leta = cancellation of the flight

So leta does not mean a different word here; it is just the case form of let.

Here, tajna is a noun, meaning secret.

So:

• je tajna = is a secret

This is important because tajna can look like an adjective form, but in this sentence it is not describing razlog directly.

If you wanted to say The reason is secret, using an adjective, you would say:

• Razlog je tajan.

Because razlog is masculine, the adjective must also be masculine: tajan, not tajna.

So:

• Razlog je tajan = The reason is secret.
• Razlog je tajna = The reason is a secret.

Croatian does not have articles like English the and a.

So nouns appear without articles, and the exact meaning depends on context.

That is why:

• razlog can mean reason or the reason
• tajna can mean a secret or sometimes the secret, depending on context

In this sentence, English most naturally uses:

• The reason for the flight cancellation is a secret.

Yes. That is also natural Croatian.

There are two common patterns:

• razlog + genitive
  → razlog otkazivanja leta
• razlog za + accusative
  → razlog za otkazivanje leta

Both mean roughly the reason for the flight cancellation.

The version without za is a bit more compact and noun-based.
The version with za may feel a little clearer to English speakers because it matches reason for more directly.

So both are good:

• Razlog otkazivanja leta je tajna.
• Razlog za otkazivanje leta je tajna.

The subject is the whole noun phrase:

• Razlog otkazivanja leta = the reason for the flight cancellation

And tajna is the predicate noun after je.

So the structure is:

• Subject: Razlog otkazivanja leta
• Verb: je
• Predicate noun: tajna

Both razlog and tajna are in the nominative, which is normal in Croatian with the verb biti (to be) in sentences like this.

Yes, Croatian word order is more flexible than English word order.

The sentence:

• Razlog otkazivanja leta je tajna.

is the most neutral and straightforward version.

You may also see different orders for emphasis, but they can change what sounds like the topic or the focus of the sentence. For a beginner, the original order is the safest one to use.

So the best takeaway is:

• Croatian allows flexibility,
• but Razlog otkazivanja leta je tajna is the normal neutral order.

In standard Croatian, the present tense of biti (to be) is normally expressed, so je should be there.

So:

• Razlog otkazivanja leta je tajna. = correct

Leaving out je would sound incomplete in standard Croatian.

This is different from some other Slavic languages where to be in the present can sometimes be omitted. Croatian normally keeps it.