Dia bukan tidak mampu, tetapi kompetensinya belum cukup.

Yes, it is a kind of double negative, and it is used deliberately.

Bukan tidak mampu literally looks like not not able, but in natural use it means something like:

• It’s not that he/she is incapable
• He/She is not exactly unable
• The problem is not total inability

This structure softens the statement. Instead of saying Dia mampu (He/She is capable), the speaker is being more careful and nuanced. It suggests:

• the person has some ability,
• but that ability is still not sufficient for the situation being discussed.

So the second half, tetapi kompetensinya belum cukup, explains the limitation more precisely.

This is a very common question.

In Indonesian:

• tidak usually negates verbs and adjectives
• bukan usually negates nouns, noun phrases, or whole identifications/assumptions

In this sentence:

• tidak mampu = not able
• bukan tidak mampu = it is not the case that he/she is not able

So bukan is negating the whole idea tidak mampu.

That is why both appear together:

• tidak negates mampu
• bukan then negates that negative statement

Mampu means able, capable, or having the capacity to do something.

It is similar to bisa, but there is a nuance:

• bisa often means general ability, possibility, or knowing how to do something
• mampu often sounds a bit more formal and can suggest capacity, capability, or adequacy

Examples:

• Dia bisa berenang. = He/She can swim.
• Dia mampu memimpin tim besar. = He/She is capable of leading a large team.

In your sentence, mampu fits well because the topic is kompetensi, which is fairly formal/professional language.

The ending -nya here means his/her.

So:

• kompetensi = competence
• kompetensinya = his/her competence

Because the sentence starts with Dia (he/she), -nya refers back to that person.

So the structure is:

• Dia = he/she
• kompetensinya = his/her competence

This is very natural in Indonesian. Instead of repeating dia again, Indonesian often uses -nya.

This is an important nuance.

• tidak cukup = not enough
• belum cukup = not enough yet

Belum suggests that the condition may change in the future. It sounds less harsh and more hopeful.

So:

• kompetensinya tidak cukup = his/her competence is insufficient
• kompetensinya belum cukup = his/her competence is not sufficient yet

In your sentence, belum cukup suggests improvement is possible.

Cukup means enough, sufficient, or adequate.

In this sentence, it means the person’s competence has not yet reached the required level.

So kompetensinya belum cukup means:

• his/her competence is not yet sufficient
• his/her competence is not enough yet

Depending on context, this could mean:

• not enough for a job,
• not enough for a task,
• not enough for promotion,
• not enough for a certain standard.

Tetapi means but.

Yes, you can often replace it with tapi:

• tetapi = more formal or careful
• tapi = more common in everyday speech

So:

• Dia bukan tidak mampu, tetapi kompetensinya belum cukup.
  sounds more formal/written
• Dia bukan tidak mampu, tapi kompetensinya belum cukup.
  sounds more conversational

Both are correct.

Yes, you could, but the nuance changes slightly.

• Dia belum cukup kompeten = He/She is not competent enough yet
• kompetensinya belum cukup = His/Her competence is not enough yet

The original sentence sounds a bit more formal and analytical because it talks about the person’s competence as a quality or measurable factor.

By contrast, Dia belum cukup kompeten describes the person more directly.

So the original can sound slightly less direct and sometimes a bit more diplomatic.

Yes. Dia can mean either he or she.

Indonesian does not normally mark gender in third-person singular pronouns the way English does. So without context, dia is gender-neutral.

That means:

• Dia bukan tidak mampu... could mean He is not exactly incapable...
• or She is not exactly incapable...

You need context to know which one is intended.

It is natural, but it leans somewhat formal or professional.

Reasons:

• mampu sounds more formal than some everyday alternatives
• tetapi is more formal than tapi
• kompetensi is a formal/professional word

This kind of sentence would fit well in:

• performance evaluations
• workplace discussions
• academic or professional contexts
• polite criticism

In everyday casual conversation, someone might say something like:

• Dia bukan nggak bisa, tapi kemampuannya belum cukup.
• Dia bisa, cuma belum cukup kompeten.

Those versions sound less formal.

Yes, but in a softened way.

The sentence does not say the person is completely incapable. Instead, it makes a more careful distinction:

• the person does have some ability,
• but their current level of competence is still insufficient.

This is a polite or diplomatic way to criticize someone’s readiness or qualifications without sounding too blunt.

So the tone is more like:

• The issue isn’t total inability; the issue is that the person is not yet sufficiently competent.

Yes, very much so.

That phrase often suggests:

• the person is not totally unable
• the person can do something
• but perhaps not at the required standard, level, or consistency

So it often carries the idea of limited ability or some ability, but not enough.

That is why the second clause is important. It clarifies the real problem:

• not absolute inability,
• but insufficient competence.

Because Dia mampu would sound stronger and more direct: He/She is capable.

The version Dia bukan tidak mampu is more cautious. It creates a more nuanced meaning, something like:

• It’s not that he/she lacks ability altogether
• I wouldn’t say he/she is incapable
• The problem lies elsewhere

This phrasing prepares the listener for the clarification in the second half. It is often used when the speaker wants to avoid sounding too absolute.