Os encargos aduaneiros são altos.

Os is the masculine plural definite article, meaning the.

It is used because encargos is a plural masculine noun. In Portuguese, articles usually agree with the noun in gender and number:

• o encargo = the charge / the burden
• os encargos = the charges / the burdens

So Os encargos aduaneiros means the customs charges/duties.

Encargos can mean charges, costs, fees, burdens, or obligations, depending on context.

In this sentence, with aduaneiros, it refers to customs charges/duties or customs-related costs.

So although the exact English translation may vary, the idea is that these are amounts imposed by customs authorities.

Aduaneiros means customs-related or related to the customs office.

It comes from aduana, which means customs.

So:

• aduana = customs
• aduaneiro / aduaneira = customs-related
• encargos aduaneiros = customs charges / customs duties

It is an adjective describing encargos.

Because it has to agree with encargos, which is masculine plural.

In Portuguese, adjectives usually agree with the noun they describe:

• encargo aduaneiro = customs charge
• encargos aduaneiros = customs charges

If the noun were feminine plural, then the adjective would also be feminine plural:

• taxas aduaneiras = customs rates/fees

São is the 3rd person plural of the verb ser in the present tense.

The subject is Os encargos aduaneiros, which is plural, so the verb must also be plural.

Present tense of ser:

• eu sou
• tu és
• ele/ela/você é
• nós somos
• vós sois
• eles/elas/vocês são

So:

• Os encargos aduaneiros são altos.
• The customs charges are high.

Here, ser is used because the sentence describes a general characteristic or inherent quality: the charges are high.

In Portuguese, ser is commonly used for:

• identity
• definition
• general characteristics
• more permanent or expected qualities

Estar is more often used for temporary states or conditions.

So são altos means the charges are high in a general sense, not just temporarily at this moment.

Altos is the masculine plural form of alto.

It agrees with encargos, which is masculine plural:

• alto = high
• alta = high (feminine singular)
• altos = high (masculine plural)
• altas = high (feminine plural)

Examples:

• O preço é alto. = The price is high.
• Os preços são altos. = The prices are high.
• A taxa é alta. = The fee/rate is high.
• As taxas são altas. = The fees/rates are high.

In this sentence, altos is not directly placed next to the noun because it is part of the predicate after ser:

• Os encargos aduaneiros = the subject
• são altos = are high

This is similar to English:

• The charges are high

If the adjective were directly attached to the noun, the structure would be different. Portuguese often places descriptive adjectives after the noun, but after a linking verb like ser, the adjective naturally comes after the verb.

Yes. The singular version would be:

• O encargo aduaneiro é alto.

That means The customs charge/duty is high.

Notice how everything changes to singular:

• Os → O
• encargos → encargo
• aduaneiros → aduaneiro
• são → é
• altos → alto

There are other common ways to express similar ideas, depending on context.

For example:

• direitos aduaneiros = customs duties
• taxas aduaneiras = customs fees/rates
• custos aduaneiros = customs costs

Encargos aduaneiros is perfectly valid, but it can sound a bit broader or slightly more formal, because encargos can cover different kinds of charges or financial burdens.

A rough European Portuguese pronunciation is:

uz en-KAR-goz a-dwa-NEI-rush soun AL-tush

A few useful points:

• Os often sounds more like uz before a vowel.
• aduaneiros has the stress on nei.
• são is nasal.
• In European Portuguese, unstressed vowels are often reduced, so the sentence may sound more compressed than a learner expects.

A more Portuguese-style approximation would be:

uz ẽ-KAR-guz a-dwɐ-NEI-rush sãw AL-tush

Usually yes, if you mean the customs charges in a normal, specific way.

Portuguese uses definite articles more often than English does. So where English might sometimes say something like Customs charges are high, Portuguese will very naturally say:

• Os encargos aduaneiros são altos.

Dropping the article can sound unnatural in many ordinary contexts, unless you are speaking in a very general, headline-like, or technical style.

Yes, but the normal and most natural order is:

• Os encargos aduaneiros são altos.

You could change the order for emphasis, but it would sound less neutral. For example:

• Altos são os encargos aduaneiros.

This is grammatically possible, but much less common in everyday speech and sounds marked or literary.

So for a learner, the standard order is definitely the one to use.