Mehanizam je skriven.

• mehanizam = mechanism
• je = is
• skriven = hidden

So the sentence literally matches English very closely: The mechanism is hidden.

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

So:

• on je = he is
• ona je = she is
• ono je = it is

In this sentence, je links the subject mehanizam with the description skriven, just like is in English.

Because skriven agrees with mehanizam.

Mehanizam is:

• masculine
• singular
• nominative (the subject form)

So the predicate adjective/participle also appears in the masculine singular form: skriven.

Compare:

• Mehanizam je skriven. = masculine singular
• Kutija je skrivena. = feminine singular
• Pismo je skriveno. = neuter singular
• Mehanizmi su skriveni. = masculine plural

It is originally a past passive participle, but in sentences like this it often functions very much like an adjective.

So Mehanizam je skriven means:

• The mechanism is hidden
• or The mechanism has been hidden, depending on context

In everyday learning terms, it is usually easiest to understand it here as an adjective-like form meaning hidden.

Usually the most natural translation is is hidden.

However, Croatian past passive participles can sometimes carry a sense close to has been hidden, especially depending on context.

Without more context, Mehanizam je skriven is best understood as:

• The mechanism is hidden

If the speaker wants to emphasize the action of hiding, other phrasing may be used.

Croatian has no articles, so there is no separate word for the or a/an.

That means mehanizam can mean:

• a mechanism
• the mechanism

Which one is meant depends on the context.

So Mehanizam je skriven could be understood as either:

• A mechanism is hidden
• The mechanism is hidden

In many learning examples, English uses the because it sounds more natural in context.

Because it is the subject of the sentence, and subjects are normally in the nominative case.

The dictionary form of the noun is also mehanizam, so this is the basic form.

If it had a different role in the sentence, it might change:

• Vidim mehanizam. = I see the mechanism.
  Here mehanizam is in the accusative, and for this noun the form happens to stay the same because it is inanimate masculine.
• Nema mehanizma. = There is no mechanism.
  Here it becomes mehanizma in the genitive.

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

The neutral order is:

• Mehanizam je skriven.

But you may also hear:

• Skriven je mehanizam.
• Je li mehanizam skriven? = Is the mechanism hidden?

Changing the order often changes the focus or emphasis, not the basic meaning.

For a learner, Mehanizam je skriven is the safest neutral pattern.

A rough pronunciation guide:

• Mehanizam ≈ meh-ha-nee-zam
• je ≈ yeh
• skriven ≈ skree-ven

A few notes:

• j in Croatian is pronounced like English y in yes
• e is usually a clear eh
• i is like ee in see
• r is rolled or tapped more than in English

So the whole sentence sounds roughly like:

meh-ha-NEE-zam yeh SKREE-ven

Yes. skriven and sakriven are both used and both can mean hidden.

Very roughly:

• skriven is extremely common and neutral
• sakriven is also common and often feels a little more directly connected with the verb sakriti (to hide)

In many contexts, they are interchangeable:

• Mehanizam je skriven.
• Mehanizam je sakriven.

Both are correct.

Normally, no.

In standard Croatian, you usually need je here because this is a normal present-tense sentence with the verb to be:

• Mehanizam je skriven.

If you say only:

• Mehanizam skriven

that sounds incomplete in standard language, except perhaps in special styles such as headlines, notes, poetry, or very informal shorthand.

The negative is:

Mehanizam nije skriven. = The mechanism is not hidden.

Here:

• nije = is not

So:

• je = is
• nije = is not

A common way is:

Je li mehanizam skriven? = Is the mechanism hidden?

This is the standard yes/no question pattern:

• Je li ... ?

In informal speech, you may also hear intonation doing some of the work, but Je li mehanizam skriven? is the form learners should know first.