Večera je ukusna, ali skupa.

Here it means dinner / supper.

A common beginner confusion is:

• veče = evening
• večera = dinner / supper

So in this sentence, večera is the meal, not the time of day.

Serbian does not have articles like English a and the.

So Večera je ukusna can mean:

• The dinner is tasty
• Dinner is tasty
• This dinner is tasty

Context tells you which meaning is intended.

Je means is. It is the 3rd person singular present form of biti (to be).

So the structure is:

• Večera = subject
• je = is
• ukusna = tasty
• skupa = expensive

Because they agree with večera, which is a feminine singular noun.

In Serbian, adjectives must match the noun in gender, number, and case.

Here:

• večera = feminine singular
• ukusna = feminine singular
• skupa = feminine singular

Compare:

• masculine: ručak je ukusan i skup = lunch is tasty and expensive
• feminine: večera je ukusna i skupa
• neuter: jelo je ukusno i skupo = the dish/food is tasty and expensive

It is in the nominative singular because it is the subject of the sentence.

The adjectives ukusna and skupa are also in nominative singular here, because they are predicate adjectives describing the subject.

Yes. Večera can also be the he/she dines / is having dinner form of the verb večerati.

But in this sentence it is clearly a noun, because the structure is:

• Večera = subject noun
• je ukusna, ali skupa = predicate

If večera were a verb here, the rest of the sentence would not fit naturally.

Because ali means but, and in Serbian it is normally preceded by a comma when it connects two contrasting parts of a sentence.

So:

• Večera je ukusna, ali skupa.

This is very normal Serbian punctuation.

Ali means but and shows a clear contrast.

So the sentence says that the dinner has one positive quality and one negative one:

• tasty, but expensive

You may sometimes hear a in similar sentences, but ali is stronger and more directly adversative. In this sentence, ali is the most natural choice if you want the clear English sense of but.

Serbian often omits repeated words when they are easy to understand.

So these two mean basically the same thing:

• Večera je ukusna, ali skupa.
• Večera je ukusna, ali je skupa.

The second je is optional here. Leaving it out sounds natural and concise.

Yes, but the given order is the most neutral.

The normal sentence is:

• Večera je ukusna, ali skupa.

You can change word order for emphasis, for example:

• Ukusna je večera, ali skupa.

That sounds more marked or stylistic.

One important point: je is a clitic, so it usually appears in the second position of its clause. That is why Večera je... sounds natural, but Večera ukusna je... does not.

Because ukusna must agree with večera.

The basic adjective is:

• masculine: ukusan
• feminine: ukusna
• neuter: ukusno

Since večera is feminine, the correct form is ukusna.

The same pattern applies to skup:

• masculine: skup
• feminine: skupa
• neuter: skupo

In this sentence, yes.

Here skupa is the feminine singular form of skup, meaning expensive.

Be aware that similar-looking forms can cause confusion:

• skup can also be a noun meaning gathering / assembly
• in some regional usage, skupa can mean together

But here, because it agrees with večera, it clearly means expensive.

A simple approximation is:

• Večera ≈ VE-che-ra
• je ≈ ye
• ukusna ≈ oo-KOOS-na
• ali ≈ A-lee
• skupa ≈ SKOO-pa

A few pronunciation notes:

• č sounds like ch in chocolate
• j sounds like English y
• u is like oo in food

So the whole sentence is approximately:

VE-che-ra ye oo-KOOS-na, A-lee SKOO-pa.