A inaptidão temporária termina no próximo mês.

Because inaptidão is a feminine singular noun, and here it is being treated as a specific condition or status: a inaptidão temporária.

In Portuguese, definite articles are used more often than in English. So where English might say just temporary incapacity, Portuguese often says a inaptidão temporária.

• a = feminine singular the
• inaptidão = a feminine noun

If the noun were masculine, you would use o instead.

Inaptidão is a fairly formal word meaning lack of fitness, inability, unsuitability, or incapacity, depending on context.

It comes from apto = fit, suitable, able.
So:

• apto = fit / suitable
• inapto = unfit / unsuitable
• inaptidão = unfitness / unsuitability / incapacity

In real life, this word often appears in administrative, medical, legal, or workplace contexts. A more everyday sentence might use another expression depending on the situation.

In Portuguese, adjectives usually come after the noun.

So:

• inaptidão temporária = temporary incapacity

That is the normal order.
You can sometimes put adjectives before the noun, but that often sounds more literary, emphatic, or changes the nuance. In this sentence, inaptidão temporária is the natural choice.

Because temporária has to agree with inaptidão, which is a feminine singular noun.

Portuguese adjectives change form to match the noun in gender and number.

• inaptidão temporária = feminine singular
• problema temporário = masculine singular
• medidas temporárias = feminine plural
• efeitos temporários = masculine plural

This agreement is very important in Portuguese.

Termina is the present indicative form of terminar, but Portuguese often uses the present tense to talk about a future event when the time is clear from context.

Here, no próximo mês already tells you the event is in the future, so termina sounds natural.

This is similar to English sentences like:

• The course ends next month.
• My contract finishes tomorrow.

You could also say:

• A inaptidão temporária terminará no próximo mês.

That is more explicitly future, but often a bit more formal.

No is a contraction of:

• em
  • o = no

So:

• no próximo mês literally = in the next month

In natural English, that is usually next month.

This happens very often in Portuguese:

• em + o = no
• em + a = na
• em + os = nos
• em + as = nas

Examples:

• no mês seguinte
• na próxima semana

Because mês is a masculine noun:

• o mês
• therefore no próximo mês

If the noun were feminine, you would use na and a feminine adjective form:

• na próxima semana

So the article and adjective both have to match the noun:

• o próximo mês
• a próxima semana

In this sentence, próximo mês most naturally means next month relative to now or to the current reference point.

Portuguese próximo can sometimes mean next or following, depending on context, but here it is straightforward.

A few useful comparisons:

• no próximo mês = next month
• no mês seguinte = the following month

Mês seguinte can sound a little more tied to a sequence in narration or formal writing.

You could also say acaba, and it would sound natural in many contexts:

• A inaptidão temporária acaba no próximo mês.

Both termina and acaba can mean ends.
The difference is mostly one of tone and style:

• termina = often a bit more neutral or formal
• acaba = often a bit more everyday

Since inaptidão temporária is itself quite formal, termina fits very well.

Yes, it sounds fairly formal and administrative.

That is mainly because of inaptidão temporária, which is not especially casual everyday vocabulary. It sounds like something you might see in:

• medical paperwork
• HR documents
• legal or official notices
• benefit or employment contexts

A more conversational sentence would depend on the exact meaning intended, but this version sounds like official language.

A helpful approximate pronunciation is:

ee-nahp-chee-DAWN or ee-nahp-tee-DAWN, depending on accent and how clearly the consonants are pronounced.

A few key points:

• The stress is on the last syllable: -dão
• The ending -ão is a nasal sound, very common in Portuguese
• English speakers often need practice not to pronounce it like a plain ow sound

A rough IPA for Brazilian Portuguese is:

/inap.tʃiˈdɐ̃w̃/ or close to that, depending on region and speech style

You do not need perfect IPA to learn it well; the main thing is:

• final stress
• nasal ão

Yes. Even if the general meaning is already known, the best English wording can change with context because inaptidão is quite broad.

Depending on the situation, it might correspond to ideas like:

• temporary incapacity
• temporary unfitness
• temporary disqualification
• temporary inability

So the Portuguese grammar is stable, but the most natural English choice depends on whether the context is medical, professional, legal, athletic, or something else.