Prije spavanja provjerim jesu li duda i čista pelena u torbi.

Because prije normally takes the genitive case in Croatian.

The base noun is spavanje = sleeping / sleep (a verbal noun from spavati = to sleep).
Its genitive singular form is spavanja.

So:

• prije = before
• spavanja = sleeping / sleep in the genitive

Literally, prije spavanja means before sleeping or before sleep. In natural English, that often becomes before going to bed or before bed, depending on context.

Provjerim is the 1st person singular present form of provjeriti.

So it means:

• provjerim = I check / I verify

The verb provjeriti is perfective, so it presents the action as a single completed check. That is why it can feel a bit like I make sure in English.

A learner may wonder why this is not provjeravam. The difference is roughly:

• provjerim = I do one complete check
• provjeravam = I am checking / I check habitually, with more focus on the process

In everyday Croatian, provjerim can sound very natural when the speaker sees this as one routine step.

Because this part of the sentence is an indirect yes/no question:

• provjerim jesu li ... u torbi
  = I check whether ... are in the bag

Croatian often uses verb + li for this kind of whether/if clause.

So:

• jesu li duda i čista pelena u torbi
  literally = are the pacifier and a clean diaper in the bag?
• after provjerim, it becomes an indirect question:
  I check whether the pacifier and a clean diaper are in the bag.

It is jesu li because the subject is plural:

• duda i čista pelena = the pacifier and a clean diaper

Even though each noun is singular by itself, together they make a compound subject, so the verb must be plural.

That is why Croatian uses:

• jesu li = whether they are

not:

• je li = whether it is

Also, in standard Croatian, with li you normally use the fuller form jesu, not su. So jesu li is the standard form here.

Because each noun refers to one item, so each noun stays singular:

• duda = one pacifier
• pelena = one diaper

But together they form a plural subject, so the verb is plural:

• jesu = are

This is similar to English:

• The pacifier and the diaper are in the bag.

The nouns are singular, but the combined subject is plural.

Because čista modifies only pelena, not both nouns.

So the phrase means:

• duda i čista pelena
  = the pacifier and a clean diaper

It does not mean:

• the clean pacifier and diaper

The adjective čista agrees with pelena only, so it is:

• feminine
• singular
• nominative

because pelena is feminine singular nominative.

They are in the nominative case because they are the subject of jesu.

So in:

• jesu li duda i čista pelena u torbi

the things being talked about as being in the bag are the pacifier and the diaper, so they appear in the nominative.

That remains true even though the clause is a question.

Because u can take two different cases depending on meaning:

• u + locative = location (in, inside)
• u + accusative = motion into something (into)

Here the meaning is location:

• u torbi = in the bag

So torbi is locative singular of torba.

Compare:

• Pelena je u torbi. = The diaper is in the bag.
• Stavljam pelenu u torbu. = I am putting the diaper into the bag.

Not completely, but the given order is very natural.

Croatian often puts the time expression first:

• Prije spavanja = Before sleeping / Before bed

And in clauses with li, the verb normally comes before li:

• jesu li ...

So this order is standard and smooth:

• Prije spavanja provjerim jesu li duda i čista pelena u torbi.

A different order is sometimes possible for emphasis, but not every rearrangement sounds natural. For example, putting the whole subject before jesu li would usually sound less neutral.

Because Croatian has no articles.

So a noun like duda can mean:

• a pacifier
• the pacifier

depending on context.

Likewise čista pelena can mean:

• a clean diaper
• the clean diaper

If Croatian needs to be more specific, it can use other words, for example:

• ta duda = that pacifier
• jedna pelena = one / a certain diaper

But in many sentences, Croatian simply leaves this to context.