Šapućemo zbog tajne.

Šapućemo is the 1st person plural present tense of šaputati, meaning to whisper.

• šaputati = to whisper
• šapućemo = we whisper / we are whispering

The ending -mo shows that the subject is we.

In Serbian, the verb ending usually already tells you the subject, so the pronoun is often omitted.

• šapućemo already means we whisper
• mi šapućemo is also possible, but it adds emphasis, contrast, or clarity

So Šapućemo zbog tajne. is perfectly natural without mi.

It can mean either one, depending on context.

Serbian present tense often covers both:

• we whisper
• we are whispering

So without extra context, šapućemo can describe a general action or something happening right now.

Because the preposition zbog requires the genitive case.

The dictionary form is:

• tajna = secret

After zbog, it changes to:

• tajne = of a secret / of the secret

So:

• zbog tajne = because of a secret / because of the secret

It is genitive singular.

The noun tajna is a feminine noun, and in the singular its genitive form is tajne.

So the pattern is:

• nominative: tajna
• genitive: tajne

Here it is genitive because of zbog.

Zbog means because of, due to, or on account of.

It introduces the reason or cause of something:

• zbog kiše = because of the rain
• zbog posla = because of work
• zbog tajne = because of a secret / because of the secret

A very important grammar point is that zbog is followed by the genitive case.

It can mean either one.

Serbian has no articles like a and the, so the phrase itself does not tell you whether the secret is specific or not. Context does that.

So:

• zbog tajne = because of a secret
• zbog tajne = because of the secret

Both are possible translations.

Because šapnemo comes from a perfective verb and usually refers to a single completed act of whispering, not an ongoing action.

• šapućemo = we whisper / we are whispering
• šapnemo = we whisper once / we say in a whisper once

In this sentence, the idea is that the whispering is the current action or manner, so šapućemo is the natural choice.

Yes. Serbian word order is fairly flexible.

The sentence:

• Šapućemo zbog tajne.

could also be:

• Zbog tajne šapućemo.

Both are grammatical, but the emphasis changes a little:

• Šapućemo zbog tajne. = neutral
• Zbog tajne šapućemo. = puts more focus on the reason

A rough guide for an English speaker:

• Š sounds like sh in shoe
• ć is a soft sound, somewhat like a very soft ch
• j sounds like y in yes

Very roughly:

• Šapućemo ≈ sha-poo-će-mo
• zbog ≈ zbog
• tajne ≈ tie-nye

So the whole sentence is approximately: sha-poo-će-mo zbog tie-nye

The exact Serbian sounds are a bit more precise than English approximations, but this will get you close.

Grammatically, radi can also mean for the sake of / because of, and it also takes the genitive. However, zbog is much more common and natural in everyday speech for a sentence like this.

So:

• Šapućemo zbog tajne. = natural, everyday Serbian
• Šapućemo radi tajne. = possible, but more formal or stylistically marked

For most learners, zbog is the better choice here.