A Ana e a Maria escrevem-se uma à outra todas as semanas.

In European Portuguese, it is very common to use the definite article before personal names: a Ana, a Maria, o João, and so on.

So A Ana e a Maria is just Ana and Maria in English. The article usually is not translated.

This is especially common in Portugal. In some contexts, the article may be omitted, but in everyday Portuguese from Portugal, this usage is very normal.

Because the subject is A Ana e a Maria, which is they.

Escrevem is the 3rd person plural present tense of escrever (to write).

• eu escrevo = I write
• tu escreves = you write
• ele/ela escreve = he/she writes
• eles/elas escrevem = they write

So A Ana e a Maria escrevem means Ana and Maria write.

Here, se shows a reciprocal meaning: the two people do the action to each other.

So escrevem-se here does not mean they write themselves. It means something like:

• they write to each other
• they write one to the other

Portuguese often uses se with plural subjects to express this kind of mutual action.

In European Portuguese, in a normal affirmative main clause, the clitic pronoun usually comes after the verb. This is called enclisis.

So:

• escrevem-se = standard European Portuguese order

You get se escrevem in other environments, especially when something triggers the pronoun to come before the verb, for example:

• não se escrevem = they do not write to each other
• quando se escrevem = when they write to each other

Also, se escrevem is much more common in Brazilian Portuguese.

Yes, they both point to the reciprocal idea, but Portuguese often uses both together for clarity.

• se already suggests a mutual action
• uma à outra makes it completely explicit: one to the other

So the sentence is very clear and natural: A Ana e a Maria escrevem-se uma à outra.

It is a bit like saying:

• They write to each other rather than just
• They write

The extra phrase helps remove any doubt.

It literally means one to the other.

In natural English, that usually becomes:

• each other
• one another

So:

• escrevem-se uma à outra = write to each other

This expression is used when two feminine people are involved.

Because the sentence is about Ana and Maria, who are both feminine.

Portuguese makes this expression agree in gender:

• uma à outra = feminine
• um ao outro = masculine

So:

• A Ana e a Maria escrevem-se uma à outra.
• O João e o Pedro escrevem-se um ao outro.

If the pair were mixed or masculine by default, Portuguese would normally use the masculine form.

Because à is a contraction of:

• the preposition a
• plus the feminine article a

So:

• a + a = à

In uma à outra, the idea is to the other one, and that requires the preposition a.

Compare:

• ao = a + o
• à = a + a

So the accent is not just decoration; it shows a real contraction.

Because escrever can be used with the meaning to write to someone.

For example:

• Escrevi à minha amiga. = I wrote to my friend.
• Ela escreve ao irmão. = She writes to her brother.

So in this sentence, uma à outra fits that pattern: each one writes to the other.

Todas as semanas means every week.

This is a common Portuguese way to express repeated frequency:

• todos os dias = every day
• todas as semanas = every week
• todos os anos = every year

But toda a semana usually means the whole week or all week, which is a different idea.

So:

• todas as semanas = every week
• toda a semana = all week / the entire week

Yes, it has some features that are especially typical of Portugal.

Two big clues are:

• A Ana, a Maria with articles before names
• escrevem-se with the pronoun after the verb

Both are very natural in European Portuguese.

In Brazilian Portuguese, you would more often hear something like:

• Ana e Maria se escrevem...

and the articles before names are less consistently used.

So the sentence is perfectly natural for Portuguese from Portugal.