Umesto da se vratimo autobusom, rezervisaćemo sedište u vozu.

Umesto da means instead of when what follows is a whole clause, not just a noun.

So:

• umesto = instead of
• da se vratimo autobusom = that we return by bus / returning by bus

Together, Umesto da se vratimo autobusom means Instead of returning by bus.

A useful comparison:

• umesto autobusa = instead of the bus
• umesto da idemo autobusom = instead of going by bus

So when Serbian needs instead of doing something, it often uses umesto da + clause.

Both word orders are possible in Serbian, but se vratimo is very common after da.

The verb is vratiti se = to return / to come back.
The particle se is part of this reflexive verb.

After da, Serbian often places short unstressed words like se early in the clause:

• da se vratimo
• da se vidimo
• da se nađemo

So da se vratimo sounds natural and standard.

This is a very common Serbian pattern. After da, Serbian usually uses a present-tense form, even when English would use an infinitive or a future-like meaning.

Here, da se vratimo does not literally mean simple present we return. In context, it means something like:

• to return
• that we return
• for us to return

So in Umesto da se vratimo autobusom, the form vratimo is grammatically present, but the overall meaning is about an action being considered as an option.

This is normal in Serbian:

• Želim da idem. = I want to go.
• Moramo da krenemo. = We have to leave.
• Umesto da čekamo... = Instead of waiting...

Because the sentence uses the perfective verb vratiti se, whose present-tense form here is vratimo.

Compare:

• vraćati se = to be returning / to return repeatedly or habitually (imperfective)
• vratiti se = to return, to come back once, as a completed action (perfective)

In this sentence, the idea is a single completed return trip, so vratiti se is the natural choice:

• da se vratimo autobusom = to return by bus

If you used vraćamo se, it would suggest an ongoing or habitual action and would not fit as well here.

Vratiti se means to return, to come back.

The se is part of the verb. Many Serbian verbs are reflexive or are simply used with se as part of their standard form.

Examples:

• vratiti = to return something, to give back
• vratiti se = to return oneself, meaning to come back

So:

• Vratio sam knjigu. = I returned the book.
• Vratio sam se kući. = I returned home.

In your sentence, se vratimo means we return / we come back.

Because Serbian uses the instrumental case to express means of transportation, especially when English uses by.

So:

• autobusom = by bus
• vozom = by train
• autom = by car
• avionom = by plane

That is why:

• vratimo se autobusom = return by bus

This is one of the most useful instrumental-case patterns to learn.

This is the future tense.

The verb is rezervisati = to reserve.
Future tense is formed with forms of hteti:

• ja ću
• ti ćeš
• on/ona/ono će
• mi ćemo
• vi ćete
• oni će

With infinitive verbs ending in -ti, Serbian often attaches the future clitic directly to the verb stem in writing:

• rezervisati + ćemo → rezervisaćemo

So:

• rezervisaćemo = we will reserve

You may also see the separated form in explanation contexts, but the standard written form here is the single word rezervisaćemo.

Yes. That is also possible.

Serbian can often express the future in two ways:

• rezervisaćemo sedište
• ćemo rezervisati sedište

Both mean we will reserve a seat.

The first one, rezervisaćemo, is very common and compact in standard written Serbian.
The second can be used too, especially when word order or emphasis calls for it.

Literally, yes, sedište is singular and means seat.

So the sentence literally says we will reserve a seat on the train.

Whether that means one seat total or one seat per person depends on context. Serbian often uses the singular in a generic or practical way where English might also do the same.

If the speaker wanted to make it clearly plural, they could say:

• rezervisaćemo sedišta = we will reserve seats

But the singular sedište is completely natural if the context already makes the number clear or if the speaker is speaking generally.

This is a classic difference between English and Serbian.

In Serbian, with trains and many enclosed vehicles, the natural expression is u + locative:

• u vozu = on the train / in the train
• u autobusu = on the bus / in the bus
• u avionu = on the plane / in the plane

So although English usually says on the train, Serbian says u vozu.

Here:

• rezervisaćemo sedište u vozu = we will reserve a seat on the train

Vozu is in the locative singular.

The preposition u can take:

• accusative when it means movement into
• locative when it means location in/inside

Here the meaning is location:

• sedište u vozu = a seat in/on the train

So u vozu uses the locative.

Compare:

• ulazimo u voz = we are getting onto/into the train (accusative, motion)
• sedimo u vozu = we are sitting on the train (locative, location)

The word order is somewhat flexible.

The original sentence is:

• Umesto da se vratimo autobusom, rezervisaćemo sedište u vozu.

But Serbian could also say:

• Rezervisaćemo sedište u vozu umesto da se vratimo autobusom.

The original version sounds very natural because it puts the contrast first:

• Instead of returning by bus...

That sets up the alternative before giving the main action.

So the word order can change, but the original order is good because it is clear and stylistically smooth.

Not in this sentence as it stands.

You need umesto da because what follows is a clause:

• da se vratimo autobusom

If you wanted to use only umesto, what follows would usually need to be a noun phrase, not a full verb clause.

For example:

• Umesto autobusa, ići ćemo vozom. = Instead of the bus, we’ll go by train.

But for instead of returning by bus, Serbian naturally uses:

• Umesto da se vratimo autobusom...

It is a standard Serbian verb, but it is a loanword based on the international word reserve.

Many such verbs are fully integrated into Serbian grammar:

• organizovati = to organize
• rezervisati = to reserve
• telefonirati = to telephone

So even though the root is not originally Slavic, the verb behaves like a normal Serbian verb:

• rezervišem
• rezervišeš
• rezervisaćemo

This is completely normal and common in everyday Serbian.