Drugačije smo planirali povratak.

Drugačije is an adverb, and here it means differently or in a different way.

It modifies planirali — so it tells us how the planning was done.

• drugačiji = different
• drugačije = differently

A very common variant is drukčije, which means the same thing.

Because smo is a clitic — an unstressed short form that normally goes in second position in the clause.

So in:

Drugačije smo planirali povratak.

the first element is drugačije, and the clitic smo comes right after it.

This is a very normal Serbian pattern. Clitics do not simply stay next to the verb the way English auxiliaries usually do.

It is understood, not stated.

Serbian often leaves out subject pronouns when the verb form already makes the subject clear. Here smo tells you it is we.

So:

• (Mi) smo planirali = We planned

You can add mi if you want emphasis or contrast:

• Mi smo drugačije planirali povratak. = We planned the return differently / It was we who planned it differently

But in ordinary speech, leaving mi out is completely natural.

It is the perfect tense, which is the normal past tense in modern Serbian.

It is formed with:

• the present tense of biti (smo = we are / here used as auxiliary)
• plus the l-participle of the main verb (planirali)

So:

• smo planirali = we planned / we were planning / sometimes we had planned, depending on context

Serbian perfect often covers several English past meanings, so the exact translation depends on the situation.

Planirali is the l-participle of planirati and agrees with the subject in number and sometimes gender.

Here, planirali suggests:

• masculine plural, or
• a mixed-gender group

If the speakers were an all-female group, you would normally get:

• Drugačije smo planirale povratak.

So Serbian past forms can show information that English does not usually show.

Povratak is in the accusative singular, because it is the direct object of planirati.

We are planning what?
→ povratak

For a masculine inanimate noun like povratak, the accusative singular looks the same as the nominative singular, so the form does not change:

• nominative: povratak
• accusative: povratak

That is why it appears unchanged.

Because Serbian has no articles like a or the.

So povratak by itself can mean:

• a return
• the return
• sometimes even our return

The exact interpretation comes from context, not from an article.

That is very normal in Serbian and something English speakers usually need time to get used to.

Yes. Serbian word order is fairly flexible, but the choice affects focus and emphasis.

For example:

• Drugačije smo planirali povratak.
  Focuses naturally on differently.

• Povratak smo planirali drugačije.
  Brings the return more into focus.

• Mi smo drugačije planirali povratak.
  Emphasizes we.

Even when the order changes, the clitic smo still tends to stay in second position.

Not necessarily.

The sentence only tells you that the return was planned in a different way. It says something about the plan, not automatically about the real outcome.

So from this sentence alone, we do not know whether:

• the return actually happened,
• the plan changed later,
• or the plan failed completely.

That would have to come from context.

Planirati is generally treated as an imperfective verb.

In this sentence, that does not stop it from being used in the past. Serbian imperfective verbs can absolutely appear in the perfect tense.

Here the focus is simply on the past act of planning:

• we planned

The sentence is about the process or fact of planning, not about a single sharply bounded completed action in the way some perfective verbs emphasize.