Estou cansado, mas mesmo assim vou estudar português hoje à noite.

Because estar is usually used for temporary states or conditions, while ser is used for more permanent characteristics.

So:

• Estou cansado = I am tired right now
• Sou cansado would sound more like I am a tired-type person or I tend to be tired, which is not what you usually mean

In this sentence, the speaker is talking about how they feel at the moment, so estou is the natural choice.

Yes. Cansado is an adjective, and it changes according to the gender of the person speaking.

• If a man is speaking: Estou cansado
• If a woman is speaking: Estou cansada

If you are talking about more than one person, it can also change for number:

• Estamos cansados = we are tired (mixed group or all male)
• Estamos cansadas = we are tired (all female)

Portuguese often omits subject pronouns when the verb already makes the subject clear.

Here, estou clearly means I am, so eu is not necessary.

• Eu estou cansado = correct
• Estou cansado = also correct, and very common

Portuguese does this much more often than English.

Mesmo assim means something like:

• even so
• even then
• all the same
• nevertheless
• still

In this sentence, it shows contrast:

• Estou cansado = I’m tired
• mas mesmo assim vou estudar = but even so I’m going to study

It adds emphasis beyond just mas. It is like saying: I’m tired, but despite that, I’ll study anyway.

A little, but in a natural way. Portuguese often uses both for emphasis.

• mas = but
• mesmo assim = even so / nevertheless

So together they create a stronger contrast:

• Estou cansado, mas vou estudar. = I’m tired, but I’m going to study.
• Estou cansado, mas mesmo assim vou estudar. = I’m tired, but even so I’m still going to study.

The second version sounds more emphatic.

This is a very common confusion for learners.

• mas = but
• mais = more

So in this sentence, mas is the conjunction introducing contrast.

Examples:

• Estou cansado, mas vou estudar. = I’m tired, but I’m going to study.
• Quero mais café. = I want more coffee.

They sound similar in many accents, so it is important to remember the spelling.

Both are possible, but vou estudar is much more common in everyday Brazilian Portuguese.

• vou estudar = literally I go to study, but it means I’m going to study
• estudarei = I will study

In modern spoken Brazilian Portuguese, the ir + infinitive structure is extremely common for future meaning.

So:

• Hoje à noite vou estudar português. = very natural, conversational
• Hoje à noite estudarei português. = correct, but more formal or literary

Because the structure is:

ir + infinitive

This is one of the main ways to talk about the future in Portuguese.

Examples:

• vou estudar = I’m going to study
• vamos sair = we’re going to go out
• ela vai trabalhar = she’s going to work

So vou is the conjugated verb, and estudar stays in the infinitive.

In Portuguese, names of languages, nationalities, and days of the week are usually not capitalized, unlike in English.

So:

• português
• inglês
• brasileiro
• segunda-feira

This is normal Portuguese spelling.

Because after the verb estudar, the language name often appears without an article.

• estudar português = to study Portuguese
• falar português = to speak Portuguese

This is very natural.

Sometimes Portuguese uses articles in places where English does not, but here português without an article is the standard choice.

Hoje à noite means tonight or this evening/tonight, depending on context.

Breakdown:

• hoje = today
• à noite = at night / in the evening

Together:

• hoje à noite = tonight

It is a very common time expression.

Because à is the contraction of:

• the preposition a
• plus the feminine article a

So:

• a + a = à

In the expression à noite, this contraction is fixed and very common.

You also see this in other time expressions:

• à tarde = in the afternoon
• à direita = to the right
• às oito = at eight o’clock

This accent is called a crase.

Yes, sometimes, but they are not always identical in use.

• hoje à noite = tonight
• esta noite = this night / tonight

In many contexts, hoje à noite is the most natural and common way to say tonight in Brazilian Portuguese.

So for a learner, hoje à noite is the safest and most natural choice here.

Yes, normally yes.

In Portuguese, mas often introduces a contrasting clause, and it is standard to place a comma before it.

So:

• Estou cansado, mas mesmo assim vou estudar...

That comma is the normal punctuation choice.

Yes. Portuguese allows some flexibility in word order, especially with time expressions.

For example:

• Estou cansado, mas mesmo assim vou estudar português hoje à noite.
• Hoje à noite, vou estudar português, mesmo estando cansado.
• Vou estudar português hoje à noite, mesmo assim.
  This one changes the nuance a bit and is less close to the original.

The original sentence is very natural and clear.

Usually cansado means tired, not specifically sleepy.

If you want to say sleepy, Portuguese more often uses:

• com sono = sleepy

So:

• Estou cansado = I’m tired
• Estou com sono = I’m sleepy

Sometimes being tired suggests sleepiness, but they are not exactly the same.

Only the adjective would need to change:

• Estou cansada, mas mesmo assim vou estudar português hoje à noite.

Everything else stays the same.

That is because cansado/cansada agrees with the speaker, but the verbs do not change for gender.