Learn Hardcore Croatian: Te cipele nisu udobne, zato na putovanje uzimam stare, ali udobne tenisice. - Those shoes are not comfortable, so for the trip I am taking old but comfortable sneakers.

Not “nije udobno”
- nije is 3rd person singular.
- udobno is neuter singular.
  This would match a neuter singular subject, e.g. To nije udobno. – That is not comfortable.
  You could say:
- Nije udobno u tim cipelama. – It’s not comfortable in those shoes.
  But that’s a different sentence structure.
Not “ne su udobne”
For biti, the negation ne is fused with the verb:
- jesu → nisu, je → nije, sam → nisam, etc.
  So ne su is ungrammatical; it must be nisu.

Could I say Te cipele su neudobne instead of Te cipele nisu udobne?

You can, and it is grammatically correct, but there is a small nuance:

Te cipele nisu udobne.
– Those shoes are not comfortable.
This is slightly softer; it just denies the quality “comfortable”, and can sound like “they’re not (really) comfortable enough”.
Te cipele su neudobne.
– Those shoes are uncomfortable.
This uses the adjective neudobne (uncomfortable) and sounds a bit stronger / more categorical: the shoes are clearly uncomfortable.

Both are fine; in everyday speech you will hear both, depending on how strong the speaker wants to be.

What does zato mean here, and what is the difference between zato and zato što?

In this sentence:

zato ≈ so / therefore / for that reason

The structure is:

Te cipele nisu udobne, zato na putovanje uzimam…
– Those shoes are not comfortable, so for the trip I (will) take…

zato stands alone and connects two independent clauses, like English so / therefore.

zato što means because and introduces a subordinate clause of reason:

Ne uzimam te cipele zato što nisu udobne.
– I’m not taking those shoes because they’re not comfortable.

So:

zato = so, therefore (starts a result clause)
zato što = because (starts a reason clause)

Why is it na putovanje and what case is used there?

Na putovanje uses:

Preposition na
- accusative (putovanje in accusative)

With na, Croatian distinguishes:

Movement toward / onto / to → na + accusative
- ići na koncert – go to a concert
- ići na posao – go to work
- ići na more – go to the seaside
- na putovanje – (for / on) a trip
Location (being at / on) → na + locative
- na koncertu – at the concert
- na poslu – at work
- na moru – at the seaside
- na putovanju – on the trip

In your sentence, na putovanje expresses destination / purpose (“for the trip”), so the accusative is used.

Why is the verb uzimam (present) used here instead of a future form like uzet ću or ponijet ću?

Uzimam is the imperfective present, and in Croatian (as in English) the present tense can be used to talk about a planned or decided future action:

Zato na putovanje uzimam stare, ali udobne tenisice.
– Literally: “Therefore, on the trip I am taking old but comfortable sneakers.”
– English equivalent: So for the trip I’m taking… / I’ll take…

Possible alternatives:

Zato ću na putovanje uzeti stare, ali udobne tenisice.
– I will take (perfective future, more “one-time, decided act”).
Zato ću na putovanje ponijeti stare, ali udobne tenisice.
– I will take/carry with me (emphasizes carrying along).

All are grammatical; uzimam sounds quite natural here and can also hint at a habit (“For trips, I take my old but comfortable sneakers”).

What case are stare, ali udobne tenisice in, and how do the adjectives agree?

They are in the accusative feminine plural as the direct object of uzimam:

Verb: uzimam (koga/što?) – I take whom/what? → tenisice

For the noun:

tenisica – one sneaker (fem. sg.)
tenisice – sneakers (fem. pl., nominative and accusative have the same form)

The adjectives must agree with tenisice in:

gender: feminine
number: plural
case: accusative

So you get:

stare tenisice – old sneakers
udobne tenisice – comfortable sneakers
stare, ali udobne tenisice – old but comfortable sneakers

Feminine plural nominative and accusative both end in -e for adjectives: stare, udobne.

Why is there a comma after stare and before ali?

Ali means but and is a coordinating conjunction that introduces a contrast. In Croatian, you normally put a comma before ali, even if it connects just two words, not entire clauses.

So:

stare, ali udobne tenisice
– old but comfortable sneakers

Here, ali joins two adjectives (stare and udobne) describing the same noun, and the comma before ali is correct and standard.

What exactly are tenisice? Do they only mean tennis shoes?

Literally, tenisice started as “tennis shoes”, but in modern Croatian the word usually means:

sports shoes / sneakers / trainers in general

So if someone says:

Nosim tenisice. – I’m wearing sneakers/trainers.

they don’t necessarily mean shoes for tennis; they mean regular sports shoes.

Regional notes:

In some regions (and in Serbian/Bosnian) you’ll also hear patike with the same meaning.
In standard Croatian, tenisice is very common and completely natural.

Why is udobne repeated after ali? Could I just say stare, ali tenisice?

You cannot say stare, ali tenisice; that would be incomplete. After ali, you still need a word that contrasts with “stare”, and it must fit grammatically.

The structure is:

stare, ali udobne tenisice
– old but comfortable sneakers

The contrast is:

old vs. comfortable

If you drop udobne, the “but” has nothing to connect to on the second side. Acceptable alternatives would be:

stare tenisice, ali su udobne. – old sneakers, but they’re comfortable.
stare, ali vrlo udobne tenisice. – old but very comfortable sneakers.

So the repetition of udobne is necessary for the sentence to be grammatical and for the contrast to be clear.

Can I move parts of the sentence around, for example: Na putovanje uzimam stare, ali udobne tenisice?

Yes. Croatian word order is fairly flexible, and several versions are grammatical. For example:

Te cipele nisu udobne, zato na putovanje uzimam stare, ali udobne tenisice.
Te cipele nisu udobne, zato uzimam na putovanje stare, ali udobne tenisice.
Te cipele nisu udobne, zato uzimam stare, ali udobne tenisice na putovanje.

All are possible, but they can slightly change emphasis:

Putting na putovanje earlier (version 1) slightly highlights the trip as the context.
Putting it at the end (version 3) can sound more like an afterthought: “I’m taking old but comfortable sneakers — for the trip.”

The original version is very natural and clear, but your suggested Na putovanje uzimam… is also perfectly fine.

Why doesn’t Croatian need a word for “the” in this sentence?

Croatian has no articles (no a/an or the) like English.

Definiteness and specificity are expressed by:

Context
- Here it’s clear we’re talking about specific shoes and sneakers.
Demonstratives (like te, ove, one)
- Te cipele = those shoes → similar to the shoes over there.
Word order and other context.

So:

Te cipele nisu udobne…
is understood as
- Those shoes / The shoes (we’re talking about) are not comfortable…

There is no separate word for the; Croatian simply doesn’t use an article.

Both cipele and tenisice are plural. How do you talk about one pair vs several pairs in Croatian?

In everyday Croatian, some clothing items are usually used in the plural even when you mean one pair, including:

cipele – shoes
tenisice – sneakers/trainers
hlače – trousers
naočale – glasses

So:

Te cipele nisu udobne.
– Those shoes are not comfortable. (normally refers to one pair)
Uzimam stare tenisice.
– I’m taking (my) old sneakers. (again, typically one pair)

If you need to be explicit about pairs, you use par (pair):

jedan par cipela – one pair of shoes
dva para tenisica – two pairs of sneakers
tri para cipela – three pairs of shoes

You can still use the singular cipela / tenisica if you literally mean one shoe:

Izgubila sam jednu tenisicu. – I lost one sneaker.
Ova cipela mi je premala. – This shoe is too small for me.

But when talking about normal wearing/using them, Croatian uses the plural form for the pair.