Ovaj plan je definitivno bolji.

Ovaj means this, so ovaj plan means this plan.

You can say just plan if the context already makes it obvious which plan you mean, but ovaj points to a specific one more clearly.

Also, ovaj has to agree with the noun:

• ovaj plan = this plan (masculine singular)
• ova ideja = this idea (feminine singular)
• ovo rešenje = this solution (neuter singular)

Because plan is a masculine singular noun in Serbian.

The demonstrative this changes form depending on the gender of the noun:

• masculine: ovaj
• feminine: ova
• neuter: ovo

Since plan is masculine, the correct form is ovaj plan.

Je is the 3rd person singular form of the verb biti (to be), so here it means is.

So the structure is:

• Ovaj plan = this plan
• je = is
• definitivno bolji = definitely better

Serbian often uses je exactly where English uses is in sentences like this.

Je is a normal present-tense form of biti in Serbian. It is not an abbreviation.

Present tense of biti:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is
• mi smo = we are
• vi ste = you are
• oni/one/ona su = they are

So je is simply the standard form for is.

Because bolji is the comparative form of dobar (good), and it is irregular.

Just like English has:

• good
• better

Serbian has:

• dobar
• bolji

So you cannot form it mechanically from dobar in the regular way. You simply learn that bolji means better.

Yes. In Serbian, adjectives usually agree with the noun in gender, number, and case.

Since plan is masculine singular, the predicate adjective here is also masculine singular:

• Ovaj plan je bolji.

Compare:

• Ova ideja je bolja. = This idea is better.
• Ovo rešenje je bolje. = This solution is better.

So:

• masculine: bolji
• feminine: bolja
• neuter: bolje

Serbian can leave that unstated, just like English can.

Ovaj plan je definitivno bolji. can mean:

• This plan is definitely better.

The comparison target may be understood from context:

• better than the previous plan
• better than your idea
• better than the old version

If you want to state it explicitly, Serbian can do that too, for example:

• Ovaj plan je bolji od onog. = This plan is better than that one.

Definitivno usually means definitely.

In this sentence it strengthens the speaker’s judgment:

• Ovaj plan je bolji. = This plan is better.
• Ovaj plan je definitivno bolji. = This plan is definitely better.

It sounds natural in everyday Serbian and works much like English definitely.

Because it modifies the adjective bolji and emphasizes the judgment.

In this sentence:

• definitivno bolji = definitely better

This placement is very natural. Serbian word order is fairly flexible, but not completely free. This version sounds neutral and standard.

You may also hear other word orders for emphasis, but Ovaj plan je definitivno bolji is the safest normal pattern.

You may hear different word orders in speech, but Ovaj plan je definitivno bolji is the most natural neutral version.

A key point is that je is a clitic, and Serbian clitics tend to stand near the beginning of the clause, often in second position. That is one reason je appears where it does.

So for a learner, the best model to use is:

• Ovaj plan je definitivno bolji.

It can change, but each version may sound more or less natural depending on emphasis.

The neutral version is:

• Ovaj plan je definitivno bolji.

A different order might emphasize something else, but learners should first master the neutral pattern: subject + je + adverb + adjective

So yes, Serbian allows flexibility, but not all possible orders are equally common or natural.

No. Serbian normally does not need a subject pronoun here.

English says:

• This plan is definitely better.

Serbian says:

• Ovaj plan je definitivno bolji.

The noun plan already tells you what the subject is, so no extra pronoun is needed.

You negate je with nije:

• Ovaj plan nije definitivno bolji.

That means:

• This plan is not definitely better, or depending on context, This plan definitely isn’t better may also be a possible interpretation in English, though Serbian intonation and context help clarify that.

If you simply want:

• This plan isn’t better, you can say:
• Ovaj plan nije bolji.

A simple pronunciation guide is:

• ovaj ≈ OH-vai or OH-vahy

More precisely:

• o as in a short clear o
• v
• aj sounding roughly like eye

So the whole word sounds close to OH-vai.

The lj in Serbian is a single sound, not a simple English l + j sequence.

A rough guide:

• bolji ≈ BOHL-yee, but with a softer l sound

The lj is similar to the soft sound in some pronunciations of million, though not exactly the same in every accent.

So:

• bo
• soft lj
• i

This sound is very common in Serbian, so it is worth practicing.

It is completely normal in everyday Serbian and also acceptable in formal contexts.

Nothing in Ovaj plan je definitivno bolji is unusually formal or slangy. It is a natural standard sentence.

The only thing to note is that definitivno can sound a bit emphatic or conversational depending on tone, but it is still standard and widely used.