Ručak je stvarno ukusan danas.

Ručak is in the nominative singular because it is the subject of the sentence: the thing being described.

• ručak = lunch
• nominative is the basic dictionary form here

In Ručak je stvarno ukusan danas, the sentence is saying something about the lunch, so nominative is the expected case.

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

So the core structure is:

• Ručak = lunch
• je = is
• ukusan = tasty

Together: Lunch is tasty.

Croatian often uses biti the same way English uses to be in sentences like this.

Because je is a clitic, and Croatian clitics usually go in the second position in the sentence or clause.

So in a neutral sentence:

• Ručak je stvarno ukusan danas.

That placement is very normal and natural.

English speakers often expect word order to work more like English, but in Croatian, short words like je follow special placement rules.

Because ukusan is an adjective agreeing with ručak.

Since ručak is:

• masculine
• singular
• nominative

the adjective also appears in the matching form:

• ukusan = masculine singular nominative

Compare:

• ručak je ukusan = the lunch is tasty
• juha je ukusna = the soup is tasty (juha is feminine)
• jelo je ukusno = the dish/food is tasty (jelo is neuter)

Ukusno would fit a neuter noun or could function differently in another context, but not with ručak.

Here stvarno means really.

It is an adverb, and it modifies ukusan:

• stvarno ukusan = really tasty

It adds emphasis, similar to English really, truly, or genuinely depending on context.

Croatian word order is more flexible than English word order. Putting danas at the end is a very natural, neutral way to add the time expression.

So:

• Ručak je stvarno ukusan danas.

sounds natural and means that today’s lunch is really tasty, or that the lunch is really tasty today.

You could move danas for emphasis:

• Danas je ručak stvarno ukusan.
• Ručak je danas stvarno ukusan.

These all mean roughly the same thing, but the emphasis shifts a little.

Not exactly in tone.

The Croatian sentence is natural, but the most natural English equivalent would usually be:

• Lunch is really tasty today.
• Today’s lunch is really tasty.

English usually would not say the lunch unless it means a very specific lunch in a particular context. Croatian does not use articles like a or the, so learners should not try to map that directly word-for-word.

Croatian has no articles like English a/an/the.

So ručak can mean:

• lunch
• the lunch
• sometimes even a lunch

depending on context.

This is very normal in Croatian. Context does the job that articles do in English.

Yes. The simpler sentence would be:

• Ručak je ukusan danas.

That means Lunch is tasty today.

Adding stvarno just makes it stronger:

• Ručak je stvarno ukusan danas. = Lunch is really tasty today.

So stvarno is optional if you do not want the extra emphasis.

A rough pronunciation is ROO-chak.

A few useful details:

• r is rolled or tapped
• u sounds like oo in food
• č sounds like ch in chocolate
• a is like a in father
• k is a clear k

Also:

• š in stvarno sounds like sh
• danas is pronounced roughly DAH-nahs

Yes. That would also be correct.

• stvarno = really
• jako = very

So:

• Ručak je stvarno ukusan danas. = Lunch is really tasty today.
• Ručak je jako ukusan danas. = Lunch is very tasty today.

Both are natural, but stvarno can sound a bit more like personal emphasis, while jako is a straightforward intensifier.