Na rukavu je mrlja od kave.

Because Croatian often puts the location first when introducing what is there.

• na = on
• rukavu = sleeve in the locative singular

So Na rukavu je mrlja od kave is literally something like:

• On the sleeve is a coffee stain

That is a completely normal Croatian way to say There is a coffee stain on the sleeve.

Because the preposition na here expresses a static location (on the sleeve), and with that meaning it takes the locative case.

The noun is:

• rukav = sleeve

In the locative singular, it becomes:

• rukavu = on the sleeve

So:

• na rukavu = on the sleeve

This is a very common pattern in Croatian:

• na stolu = on the table
• na zidu = on the wall
• na rukavu = on the sleeve

It is locative singular.

Here is the breakdown:

• rukav = masculine noun
• after na meaning on / at in a fixed place, Croatian uses the locative
• so rukav → rukavu

This is one of the first important preposition-case combinations to learn:

• na + locative = location
• na + accusative = movement toward a surface/place

Compare:

• Na rukavu je mrlja. = The stain is on the sleeve.
• Stavio je značku na rukav. = He put the badge onto the sleeve.

Croatian does not use a direct equivalent of English there is in the same way.

Instead, Croatian often just uses to be:

• Na rukavu je mrlja od kave.
• literally: On the sleeve is a coffee stain.

This is the normal Croatian structure.

You may also hear ima in some contexts, but here je is the most natural choice.

Because mrlja is the subject of the sentence.

The basic structure is:

• Na rukavu = location
• je = is
• mrlja od kave = a coffee stain

So the thing that is somewhere is mrlja, and subjects are in the nominative.

That is why it is:

• mrlja = nominative singular

not:

• mrlju = accusative singular

Here od means something like from or of, but in natural English we translate it as coffee in coffee stain.

So:

• mrlja od kave = stain from coffee = coffee stain

Croatian very often uses od + genitive for this kind of idea:

• čaša od vina = a wine glass / a glass for wine / a glass with wine contextually
• miris od luka is less standard than miris luka, but learners often notice similar patterns
• mrlja od ulja = oil stain
• mrlja od krvi = blood stain

In this sentence, od kave tells you what caused the stain.

Because od requires the genitive case.

The base noun is:

• kava = coffee

After od, it becomes:

• kave = of/from coffee

So:

• od kave = from coffee

This is a very common pattern:

• od vode = from water
• od čokolade = from chocolate
• od vina = from wine

Usually mrlja od kave is the most natural everyday way to say coffee stain.

mrlja kave is not the usual neutral phrase here. It can sound less idiomatic or more like a quantity/trace/stain of coffee itself, depending on context.

So for a learner, the safest choice is:

• mrlja od kave = coffee stain

This is the expression you are most likely to hear and use.

Because je is a clitic in Croatian. Clitics usually go in the second position of the sentence or clause.

In this sentence, the first unit is:

• Na rukavu

Then the clitic comes:

• je

Then the rest:

• mrlja od kave

So:

• Na rukavu je mrlja od kave.

This second-position tendency is very important in Croatian word order.

Yes. Croatian word order is fairly flexible, but different orders change the focus or emphasis.

For example:

• Na rukavu je mrlja od kave.
  Neutral; focuses first on the location.

• Mrlja od kave je na rukavu.
  Focuses more on the coffee stain.

• Na rukavu je od kave mrlja.
  Grammatically possible in some expressive contexts, but not the normal neutral order.

For everyday use, the original sentence is very natural.

Because Croatian has no articles.

English distinguishes:

• a sleeve
• the sleeve
• a stain
• the stain

Croatian does not normally do this with separate words. Context tells you whether something is definite or indefinite.

So:

• rukav / rukavu can mean a sleeve / the sleeve
• mrlja can mean a stain / the stain

In this sentence, English would often say:

• There is a coffee stain on the sleeve

But Croatian simply says:

• Na rukavu je mrlja od kave.

Very often, yes, but not always in exactly the same way as English on.

Here it works straightforwardly:

• na rukavu = on the sleeve

But more generally, Croatian prepositions do not always match English one-for-one. For example, Croatian may use na, u, or another preposition where English uses on, in, or at depending on the situation.

In this sentence, na is the correct and natural choice because a stain is on a surface.

Yes, it is completely natural and idiomatic.

It sounds like a normal sentence you might say if you notice a stain on someone’s clothing.

You could also say similar things like:

• Na košulji je mrlja od vina. = There is a wine stain on the shirt.
• Na hlačama je mrlja od ulja. = There is an oil stain on the trousers.

So the pattern is very useful and common.