Não vamos estragar a surpresa de aniversário da Maria.

Because vamos is the 1st person plural form of ir (to go), and Portuguese often uses:

ir + infinitive

to talk about the near future or an intention.

So:

• vamos estragar = we are going to spoil / ruin
• não vamos estragar = we are not going to spoil / ruin

This is very common in everyday Portuguese. A simpler future tense also exists:

• não estragaremos

but that sounds more formal or less conversational than não vamos estragar.

In Portuguese, não normally goes before the conjugated verb to make the sentence negative.

So:

• vamos estragar = we are going to spoil
• não vamos estragar = we are not going to spoil

Here, não negates the whole verbal idea, not just estragar.

It is built into the verb vamos.

Portuguese often drops subject pronouns when the verb ending already makes the subject clear. So:

• vamos already means we go / we are going
• nós vamos is possible, but nós is often omitted

So the full idea is:

• (Nós) não vamos estragar...

with nós understood.

Because after vamos in this future construction, Portuguese uses the infinitive of the main verb.

Pattern:

• ir + infinitive
• vamos comer = we are going to eat
• vamos sair = we are going to leave
• vamos estragar = we are going to spoil

So estragar stays in its basic dictionary form.

Estragar usually means to spoil, to ruin, or to mess up.

In this sentence, it means:

• to ruin the surprise
• to spoil the surprise

It does not mean physically damaging something here. It means ruining the effect of the surprise, for example by revealing it too early.

Because Portuguese often uses the definite article where English may or may not use one.

Here, a surpresa means the surprise. It refers to a specific, known surprise.

Also, surpresa is a feminine singular noun, so the article must be:

• a = feminine singular the

If it were masculine, it would be o.

Literally, de aniversário means of birthday, but in natural English it corresponds to birthday.

So:

• surpresa de aniversário = birthday surprise

This de + noun structure is very common in Portuguese.

Examples:

• bolo de chocolate = chocolate cake
• festa de aniversário = birthday party
• presente de Natal = Christmas present

So de aniversário describes what kind of surprise it is.

Not necessarily.

Surpresa de aniversário means birthday surprise in a general sense. It could be a gift, a plan, an event, or a party.

If you specifically want to say surprise party, Portuguese would more naturally use:

• festa surpresa
• or festa de surpresa in some contexts

So this sentence does not automatically mean there is a party. It only tells us there is some kind of birthday surprise.

Because da is a contraction of:

• de + a = da

In European Portuguese, personal names often take the definite article:

• a Maria
• o João

So:

• de + a Maria becomes da Maria

That is why the sentence has da Maria.

This is especially common in Portugal. In other varieties, especially in some Brazilian usage, the article with names may be less regular.

In this sentence, da Maria is best understood as Maria’s in English:

• a surpresa de aniversário da Maria = Maria’s birthday surprise

But the meaning is really one of association, not strict ownership. It refers to the surprise connected with Maria’s birthday, usually the surprise intended for her.

English often uses the possessive:

• Maria’s birthday surprise

Portuguese often uses a de phrase:

• a surpresa de aniversário da Maria

So although it looks like of Maria word-for-word, the natural English translation is usually Maria’s.

A rough European Portuguese pronunciation would be something like:

não vâ-mush esh-tra-GAR a sur-PRAY-zɐ d(a) a-nee-ver-SAH-ryu dɐ ma-REE-a

A few useful pronunciation notes:

• não has a nasal sound, not a clear English now
• vamos often sounds closer to vâ-mush in European Portuguese
• the s at the end of vamos sounds like sh before the next consonant
• unstressed vowels are often reduced, especially in European Portuguese
• Maria is pronounced with the stress on ri: Ma-RI-a

So the written form is straightforward, but the spoken European Portuguese version is more reduced than an English speaker might expect.