Learn Hardcore Croatian: Ne zaboravi ruksak; šalica je unutra. - Don’t forget the backpack; the cup is inside.

It’s the 2nd person singular imperative of zaboraviti (perfective “to forget”), addressing one person (ti). Plural/formal: zaboravite. First-person “let’s” form: zaboravimo (e.g., as a suggestion).

Can I say Nemoj zaboraviti ruksak instead of Ne zaboravi ruksak?

Yes. Both are correct.

Ne + imperative (Ne zaboravi) is shorter and can sound more direct.
Nemoj + infinitive (Nemoj zaboraviti) is very common in instructions and can feel a bit softer. Plural/formal: Nemojte zaboraviti.

Why is ruksak unchanged—why not ruksaka?

Because it’s a direct object (accusative) and it’s an inanimate masculine noun. In Croatian, inanimate masculine nouns have the same form in nominative and accusative singular: ruksak. Forms like ruksaka are used in other cases (e.g., genitive).

So when would I say ruksaka, ruksaku, ruksakom?

Genitive: ruksaka (e.g., bez ruksaka “without the backpack”).
Dative/Locative: ruksaku (e.g., u ruksaku “in the backpack” [location]).
Instrumental: ruksakom (e.g., s ruksakom “with a backpack”).

Why is it šalica and not šalicu?

Here šalica is the subject (nominative) of the clause with je. If it were a direct object, it would be šalicu (accusative), e.g., Stavi šalicu u ruksak.

Could I say u ruksaku, u njemu, or unutar ruksaka instead of unutra?

Yes, with slightly different flavors:

u ruksaku = explicitly “in the backpack” (locative).
u njemu = “in it,” referring back to ruksak (locative of the pronoun).
unutar ruksaka = “inside the backpack” (more formal; genitive after unutar).
unutra is a bare adverb “inside,” relying on context for “inside what.”

What exactly is unutra grammatically?

It’s an adverb meaning “inside.” It does not take an object. If you want to name the container, use:

u + Locative (e.g., u ruksaku), or
unutar + Genitive (e.g., unutar ruksaka). Colloquial redundancy like unutra u ruksaku is heard but stylistically loose.

Is the word order fixed? Can I say Unutra je šalica?

Both Šalica je unutra and Unutra je šalica are correct. Fronting unutra emphasizes the location (“Inside is where it is”), while the original order neutrally states where the cup is.

Is the semicolon normal in Croatian here?

Yes. Croatian uses semicolons much like English to join two closely related independent clauses. Alternatives:

A period: Ne zaboravi ruksak. Šalica je unutra.
A dash: Ne zaboravi ruksak — šalica je unutra.
A conjunction: Ne zaboravi ruksak, jer je šalica unutra.

How do articles work here—how do I know if it’s “the” cup or “a” cup?

Croatian has no articles. Definiteness comes from context. Mentioning the backpack first makes a specific, known cup the natural interpretation in the second clause.

Should I add tvoj or svoj to say “your backpack”?

Usually you omit it in imperatives; Ne zaboravi ruksak is understood as “your backpack.” If you add one:

svoj ruksak = “your own backpack” (reflexive, preferred when the subject is “you”).
tvoj ruksak can sound contrastive (your backpack as opposed to someone else’s).

How would I turn the second clause into a yes–no question?

Use Je li: Je li šalica unutra? Colloquial contraction: Je l’ šalica unutra? (In Croatian, Je li is the standard; Da li is common colloquially/regionally but less standard in Croatian.)

What is je doing, and why is it in that position?

je is the clitic form of the verb biti (“to be”) in the 3rd person singular. Croatian clitics tend to appear in second position in the clause. Hence:

Šalica je unutra
Unutra je šalica In both, je sits after the first stressed element.

Which case does u take—accusative or locative?

u + Accusative = motion into: Stavi šalicu u ruksak.
u + Locative = location in: Šalica je u ruksaku.

Is Ne zaboravi too blunt? How can I soften it?

You can soften with molim or nemoj:

Molim te, ne zaboravi ruksak.
Nemoj zaboraviti ruksak, molim te.
Formal/plural: Molim vas / Nemojte zaboraviti ruksak.

Are there regional words for šalica?

Yes. šalica is standard in Croatian. In Serbian/Bosnian you’ll often hear šolja. Related items: čaša (drinking glass), krigla (beer mug/stein).