Eu vou pagar a mensalidade do curso de português amanhã.

Yes, you often can leave it out in Portuguese.

Portuguese is a pro-drop language, which means the subject pronoun is often omitted when the verb already makes the subject clear. So:

• Eu vou pagar a mensalidade do curso de português amanhã.
• Vou pagar a mensalidade do curso de português amanhã.

Both are natural.

Including Eu can add:

• emphasis
• contrast
• clarity

For example, Eu vou pagar amanhã can sound like I’m the one who will pay tomorrow or I will pay tomorrow.

Vou pagar is a very common way to talk about the near future in Brazilian Portuguese.

It is formed with:

• ir in the present tense: vou
• • the infinitive: pagar

So:

• vou pagar = I’m going to pay / I will pay

This is similar to English going to pay.

Portuguese also has a simple future:

• pagarei

But in everyday Brazilian Portuguese, vou pagar is usually more common and more natural in conversation.

Mensalidade means a monthly fee or monthly payment.

It is used for things you pay every month, such as:

• tuition
• a gym membership
• a school fee
• a course fee

In this sentence, a mensalidade do curso means the monthly fee for the course.

It does not just mean any payment. It specifically suggests something paid on a monthly basis.

Here, a is the feminine singular definite article, meaning the.

• a mensalidade = the monthly fee

The noun mensalidade is feminine, so it takes a, not o.

This article is very normal in Portuguese. Portuguese uses definite articles more often than English does, so where English might sometimes say just tuition or course fee, Portuguese often says a mensalidade.

Do is a contraction of:

• de + o = do

So:

• do curso = of the course

This contraction is mandatory in standard Portuguese.

Other common contractions are:

• de + a = da
• de + os = dos
• de + as = das

So you say:

• a mensalidade do curso not
• a mensalidade de o curso

Because de português here means of Portuguese in the sense of a Portuguese course / a course in Portuguese.

When naming a subject, language, or area of study, Portuguese often uses de + subject without an article:

• curso de português
• aula de inglês
• livro de história

Using do português would usually sound different and more specific, as if you were referring to the Portuguese language in a more particular way, not just naming the subject of the course.

So curso de português is the natural expression for Portuguese course.

In Portuguese, names of languages are normally not capitalized unless they begin a sentence.

So:

• português
• inglês
• espanhol

This is different from English, where language names are capitalized:

• Portuguese
• English
• Spanish

So curso de português is correct.

Amanhã is flexible in Portuguese.

Your sentence has:

• Eu vou pagar a mensalidade do curso de português amanhã.

That is completely natural.

You could also say:

• Amanhã eu vou pagar a mensalidade do curso de português.
• Eu amanhã vou pagar a mensalidade do curso de português.

The most common placements are usually:

• at the end
• at the beginning

Putting amanhã first often gives it a little more emphasis:

• Tomorrow, I’m going to pay...

Mostly yes, but there are some differences.

In this sentence:

• pagar a mensalidade = pay the monthly fee

That structure is very normal: pagar + thing

Examples:

• pagar a conta = pay the bill
• pagar o aluguel = pay the rent
• pagar a mensalidade = pay the monthly fee

If you want to mention the person receiving the money, Portuguese may use a:

• pagar ao professor
• pagar à escola

So pagar works similarly to English, but the exact prepositions can vary depending on what comes after it.

Yes, that is grammatically correct.

• Eu pagarei a mensalidade do curso de português amanhã.

This is the simple future tense.

However, in everyday Brazilian Portuguese, vou pagar is usually more common and more natural than pagarei.

Very roughly:

• vou pagar = more common in speech, everyday, natural
• pagarei = a bit more formal, written, or emphatic in many contexts

Both mean the same basic thing here.

Yes, it is perfectly natural in Brazilian Portuguese, and it would also be understood in other varieties of Portuguese.

A few points that feel especially normal in Brazilian usage:

• the future with vou pagar
• the straightforward word order
• the use of mensalidade for a recurring monthly course fee

So if you are learning Brazilian Portuguese, this sentence is an excellent, natural model.

It would sound very natural:

• Vou pagar a mensalidade do curso de português amanhã.

In conversation, this is probably the version you would hear most often unless the speaker wants emphasis.

Portuguese speakers do not need to say the pronoun every time, because vou already tells you the subject is I.

That information comes from:

• do curso de português

This breaks down as:

• curso = course
• de português = of Portuguese / in Portuguese

So:

• a mensalidade do curso de português = the monthly fee for the Portuguese course

The phrase de português modifies curso, telling you what kind of course it is.