Learn Hardcore Croatian: Svaka rečenica u udžbeniku je važna. - Every sentence in the textbook is important.

svaka rečenica = every sentence (focus on each individual sentence, singular)
sve rečenice = all the sentences (focus on the group as a whole, plural)

Svaka is the feminine singular form of the determiner/pronoun svaki (“every, each”). It must agree in gender and number with rečenica (which is feminine singular). That’s why we say:

Svaka rečenica je važna. – Every sentence is important.
Sve rečenice su važne. – All (the) sentences are important.

Why is it svaka rečenica and not svaki rečenica?

In Croatian, determiners and adjectives agree with the noun in gender, number and case.

rečenica is a feminine noun.
svaki is the masculine form (“every” for masculine nouns).
The feminine form of svaki is svaka.

So you must match the gender:

svaki student (masculine) – every (male) student
svaka rečenica (feminine) – every sentence
svako dijete (neuter) – every child

If we are talking about many sentences, why is the verb je (singular) and not su (plural)?

Grammatically, the subject of the sentence is svaka rečenica – which is singular, not plural.

Even though the idea refers to all sentences, the structure is “each individual sentence”. Croatian verbs agree with the form of the subject, not with the “conceptual” plurality.

Compare:

Svaka rečenica je važna. – Every sentence is important.
- Subject: svaka rečenica (singular) → verb: je (3rd person singular)
Sve rečenice su važne. – All sentences are important.
- Subject: sve rečenice (plural) → verb: su (3rd person plural)

Why does važna end in -a and not -an or -o?

Važna is the feminine singular form of the adjective važan (“important”).

Adjectives must agree with the noun:

Masculine singular: važan (e.g. važan tekst – important text)
Feminine singular: važna (e.g. važna rečenica – important sentence)
Neuter singular: važno (e.g. važno pitanje – important question)

Because rečenica is feminine singular, you need važna:

Svaka rečenica je važna.

What case is rečenica in here, and why?

Rečenica is in the nominative singular.

Reasons:

It is the subject of the sentence.
The basic dictionary form of a noun is also the nominative singular.

So:

Nominative singular: rečenica – subject: Svaka rečenica u udžbeniku je važna.
Other cases change it (e.g. rečenicu, rečenice, etc.), but here you need the basic subject form.

A mini declension (singular only) for reference:

Nominative: rečenica – (tko/što?) rečenica
Genitive: rečenice – (koga/čega?) rečenice
Dative: rečenici – (komu/čemu?) rečenici
Accusative: rečenicu – (koga/što?) rečenicu
Locative: rečenici – (o komu/čemu?) o rečenici
Instrumental: rečenicom – (s kim/čim?) s rečenicom

What case is used in u udžbeniku, and why is it not u udžbenik?

U udžbeniku uses the locative case.

The preposition u (“in, into”) can take:

Accusative = movement into something (u udžbenik – into the textbook)
Locative = location in something (u udžbeniku – in the textbook)

Here we are describing where the sentences are (a static location), not movement, so we use locative:

Svaka rečenica u udžbeniku je važna. – Every sentence in the textbook is important. (location)
Stavili smo to u udžbenik. – We put that into the textbook. (movement → accusative: udžbenik)

Can I change the word order, for example: Svaka rečenica je važna u udžbeniku or U udžbeniku je svaka rečenica važna? Does the meaning change?

All of these are grammatically correct, but the focus changes slightly:

Svaka rečenica u udžbeniku je važna.
Neutral, slightly emphasizes the sentences in the textbook.
Svaka rečenica je važna u udžbeniku.
Can sound like you are contrasting u udžbeniku with somewhere else, as in:
“Every sentence is important in the textbook (there, specifically).”
U udžbeniku je svaka rečenica važna.
Puts u udžbeniku in the foreground:
“In the textbook, every sentence is important.”

The basic meaning stays the same, but word order in Croatian is often used to highlight different parts of the message.

Could you omit je and just say Svaka rečenica u udžbeniku važna?

In standard Croatian, you should not omit the verb je here. The correct full sentence is:

Svaka rečenica u udžbeniku je važna.

You might see je omitted in headlines, notes, or very informal speech/writing:

Svaka rečenica važna!

But in normal, full sentences, the copula biti (“to be”) is used:

rečenica je važna – the sentence is important

How would you say “All the sentences in the textbook are important” instead of “Every sentence in the textbook is important”?

You would make both the subject and adjective plural:

Sve rečenice u udžbeniku su važne.

Changes:

Svaka rečenica → Sve rečenice (from singular every sentence to plural all sentences)
je → su (3rd person singular → plural)
važna → važne (feminine singular adjective → feminine plural)

So we have:

Svaka rečenica u udžbeniku je važna. – Every sentence in the textbook is important.
Sve rečenice u udžbeniku su važne. – All (the) sentences in the textbook are important.

What does udžbenik mean exactly, and is it different from knjiga?

udžbenik = textbook, a book specifically designed for teaching/learning a subject.
knjiga = book in general.

So:

Svaka rečenica u udžbeniku je važna. – Every sentence in the textbook is important.
Svaka rečenica u knjizi je važna. – Every sentence in the book is important. (more general; could be any kind of book)

The original sentence highlights that this is a learning/teaching book, not just any book.

How do you pronounce udžbenik, especially the džb part?

Udžbenik is pronounced roughly as:

/ʊdʒ-be-nik/

Key points:

u – like “oo” in book (short)
dž – a single sound, like “j” in jam or “g” in gin
b – as in English book
e – like “e” in bed
nik – “neek” (short i, not like English “ee” in length)

Syllable division: ud-žbe-nik.

The letter pair dž is considered one consonant in Croatian (like č or š), so udžbenik has 8 letters but 7 sounds.