Learn Hardcore Portuguese (Portugal): Para um adulto cansado, um fim de semana sem trabalho é perfeito. - For a tired adult, a weekend without work is perfect.

Using por (por um adulto cansado) would be wrong here, because por is used more for ideas like “by / through / because of” (agent, cause, means), not for “for (someone)” in the sense of beneficiary or target.

So:

para um adulto cansado = “for a tired adult” (appropriate for them)
por um adulto cansado = ungrammatical in this meaning

Why is it um adulto cansado and not um cansado adulto, like “a tired adult” in English?

In Portuguese, adjectives normally follow the noun:

um adulto cansado (literally “an adult tired”)

Putting the adjective before the noun (um cansado adulto) is either:

wrong-sounding, or
extremely marked / poetic / unusual in this case.

The natural, neutral order is:

um adulto cansado = “a tired adult”

Some common adjectives can appear before the noun and change nuance (e.g. um grande homem vs um homem grande), but cansado is not usually put before adulto in normal speech.

Why is it adulto and cansado (masculine) and not adulta and cansada?

In Portuguese, adjectives must agree in gender and number with the noun they describe.

adulto is a masculine singular noun (“(a) male adult” or a grammatically masculine “adult”)
cansado is the masculine singular form of the adjective “tired”

So:

um adulto cansado = a tired (male / grammatically masculine) adult
uma adulta cansada = a tired (female / grammatically feminine) adult

If you want to talk specifically about a woman, you would say:

Para uma adulta cansada, um fim de semana sem trabalho é perfeito.
“For a tired (female) adult, a weekend without work is perfect.”

How would I say this sentence in the plural, like “For tired adults, weekends without work are perfect”?

You need to pluralize all the relevant words and keep agreement:

Para adultos cansados, fins de semana sem trabalho são perfeitos.

Changes:

um adulto → adultos
cansado → cansados
um fim de semana → fins de semana (irregular plural: fim → fins)
é perfeito → são perfeitos

This keeps masculine plural agreement throughout (you could do adultas cansadas / perfeitas for a group of only women).

Why do we repeat um: um adulto cansado, um fim de semana? Could we say Para adulto cansado, fim de semana sem trabalho é perfeito?

The articles here are obligatory in standard Portuguese:

um adulto cansado = “a tired adult”
um fim de semana = “a weekend”

Leaving out the indefinite articles the way you did:

Para adulto cansado, fim de semana sem trabalho é perfeito

sounds very unnatural or incorrect in European Portuguese. Portuguese uses articles much more than English, especially with countable singular nouns.

So you normally must say:

Para um adulto cansado, um fim de semana sem trabalho é perfeito.

What exactly does fim de semana mean, and how do we form the plural?

fim de semana literally means “end of week” and is the normal word for “weekend” in European Portuguese.

Spelling:

Modern standard spelling is fim de semana (separate words).
Older spelling fim‑de‑semana (with hyphens) is still seen, but the no‑hyphen version is now standard.

Plural:

o fim de semana → os fins de semana (note fim → fins)
Example:
Gosto de passar os fins de semana em casa.
“I like to spend weekends at home.”

Why is it sem trabalho (“without work”) and not sem trabalhar (“without working”)? Are both possible?

Both structures exist, but they are not identical in nuance.

sem trabalho = “without work” (no work, no job, no tasks)
- Focus on the absence of work as a thing.
sem trabalhar = “without working” (without doing the action)
- Focus on the absence of the activity.

In this sentence:

um fim de semana sem trabalho suggests “a weekend with no work to do” (no shifts, no tasks, no obligations).
um fim de semana sem trabalhar would sound more like “a weekend without doing any work”, focusing more explicitly on the action of working.

Both are grammatically fine; sem trabalho is a bit more neutral and idiomatic here.

Why is it é perfeito and not está perfeito?

Portuguese distinguishes ser and estar:

ser = inherent, general, more permanent characteristic
estar = temporary state, situation right now

Here we’re making a general statement:

Um fim de semana sem trabalho é perfeito (para um adulto cansado).
“A weekend without work is perfect (for a tired adult).”

We’re saying that such a weekend is (by nature) perfect for a tired adult, not just in a specific moment.

If you used está perfeito, you’d be describing a current specific situation (“this particular weekend is perfect”), which is a different meaning and context:

Este fim de semana está perfeito.
“This weekend is perfect (right now / as things are).”

Can I change the word order and say Um fim de semana sem trabalho é perfeito para um adulto cansado? Does it change the meaning?

Yes, that version is perfectly correct:

Um fim de semana sem trabalho é perfeito para um adulto cansado.

Both sentences mean the same thing. The difference is mainly in emphasis / information structure:

Para um adulto cansado, um fim de semana sem trabalho é perfeito.
- Starts with “For a tired adult”.
- Emphasizes the point of view of the adult.
- Feels a bit more “framed” or contrastive: “As for a tired adult…”
Um fim de semana sem trabalho é perfeito para um adulto cansado.
- Starts with “A weekend without work”.
- Emphasizes the weekend itself and then says for whom it’s perfect.
- Slightly more neutral, typical word order.

Both are natural in European Portuguese.

Why is there a comma after Para um adulto cansado?

Para um adulto cansado is a prepositional phrase placed at the beginning of the sentence for emphasis (“For a tired adult…”). In Portuguese, when such introductory phrases are moved to the front, it’s very common (and usually recommended) to separate them with a comma:

Para um adulto cansado, um fim de semana sem trabalho é perfeito.

Without the comma, it’s not exactly wrong in casual writing, but it looks less standard and can be harder to read. The comma marks a slight pause and clarifies the sentence structure.

How do you pronounce the sentence in European Portuguese?

An approximate IPA transcription for European Portuguese:

Para um adulto cansado, um fim de semana sem trabalho é perfeito.

/ˈpaɾɐ ũ ɐˈðuɫtu kɐ̃ˈsaðu | ũ ˈfĩ dɨ sɨˈmɛnɐ sɐ̃j̃ tɾɐˈβaʎu ɛ pɨɾˈfɐjtu/

A few tips (simplified):

r in para, perfeito is usually a soft, single tap [ɾ].
um is nasal: vowel similar to “oo” but nasalized.
adulto: stress on -dul-: a‑DUL‑to.
cansado: stress on -sa-: can‑SA‑do.
fim de semana: stress on -me-: fi‑m de se‑MA‑na.
trabalho: tra‑BA‑lho, with lh as the palatal sound [ʎ], like Italian gli.
perfeito: per‑FEI‑to, with ei like “ay” in “say”.

Native speech will also link words, e.g. para um sounding like parum, sem trabalho like sentrabálho.

Why is it sem trabalho and not sem o trabalho?

The choice between trabalho and o trabalho depends on how specific you want to be:

sem trabalho = “without work” in general; no work, no job tasks.
sem o trabalho = “without the work” – referring to some specific work: your job, a particular project, etc.

In this generic, typical-situation sentence, we’re speaking about work in general that an adult normally has, so sem trabalho is more natural.

If you were talking about someone's particular job, you might say:

Um fim de semana sem o trabalho é raro.
“A weekend without (that) work is rare.”

Is perfeito agreeing with fim de semana? Does it change to perfeita in any situation?

Yes. Perfeito is an adjective and agrees with the subject:

Subject here: um fim de semana (masculine singular)
So the adjective is masculine singular: perfeito

If the subject were feminine, the adjective would also be feminine:

Uma semana sem trabalho é perfeita.
“A week without work is perfect.”

Plural example:

Fins de semana sem trabalho são perfeitos.
“Weekends without work are perfect.”

So:

masculine singular: perfeito
feminine singular: perfeita
masculine plural: perfeitos
feminine plural: perfeitas