"Have cooked lunch" pode ser traduzido como "almoçou"?

Não. Almoçar = Eat/have lunch. O google tradutor oferece traduções erradas muitas vezes.

In English it´s not usual a sentence without the subject/who does the action.
So, here lacks something like "I have just cooked the lunch", for intance.
By the way, I would say that "I have...cooked" isn´t the most common sentence found in English, it would be important to know what you mean in Portuguese (context included) so we could answer in a more accurate way.

What Leonardo pointed out is true, sometimes Google is not the sharpest knfe in the drawer when it comes to translation/version from one language into the other.
The very fact of "having" in the sense of "comer" (if is the case with the question) would be normal to say "I had lunch" (lunch - we assume is cooked, but if one don´t mean that would specify that it was "raw food", or something like that). So, it would be "I had raw food for lunch."
See? We don´t know if you mean "have" or "had", that what I call a broad question. Broad questions prompt a variety of acceptable and generally unpredictable responses..

Muito obrigada pela explicação!

Realmente minha pergunta ficou fora de contexto... A frase completa seria:
"Maria and John have cooked lunch, now they can play outside."
Esse seria o contexto. É uma frase pronta que encontrei buscando exercícios em inglês. Como o contexto diz que eles agora podem brincar lá fora, dá a entender que Maria e John são crianças, e assim, provavelmente, eles não fizeram o almoço, ou seja, dá a entender que a tradução do Google "almoçaram" está correta. Mas fiquei em grande dúvida.

PPAULO escreveu: 15 Mar 2020, 18:39 In English it´s not usual a sentence without the subject/who does the action.
So, here lacks something like "I have just cooked the lunch", for intance.
By the way, I would say that "I have...cooked" isn´t the most common sentence found in English, it would be important to know what you mean in Portuguese (context included) so we could answer in a more accurate way.

What Leonardo pointed out is true, sometimes Google is not the sharpest knfe in the drawer when it comes to translation/version from one language into the other.
The very fact of "having" in the sense of "comer" (if is the case with the question) would be normal to say "I had lunch" (lunch - we assume is cooked, but if one don´t mean that would specify that it was "raw food", or something like that). So, it would be "I had raw food for lunch."
See? We don´t know if you mean "have" or "had", that what I call a broad question. Broad questions prompt a variety of acceptable and generally unpredictable responses..

There's no indication to the fact of Maria and John being children, "play" also may have the meaning of "jogar" (play handball, basketball, volleyball, etc), they could be (adult) friends or a romantic couple.

So, they prepared/have prepared the lunch and now they can play outside or take part in any other outdoor activity.

Notice that I didn't assume a verb tense, so I left for you to decide if they prepared/have prepared.

I only helped you to make sense of the sentence.

Ref. cursodeingles

"Play outside" definitely implies that they're children, but there's no reason children can't cook lunch!

Agreed, most of the time Bryan, and perhaps 99.9999%...
The problem is that not always the Brazilian test-maker remind himself of some differences in nuances. Case in point, I think they meant "play outdoors" but in haste they wrote "play outside". Not necessarily because they forgot, but the language notions are very close in Portuguese.
That´s likely to be the case. It´s so close and used as such in Portuguese that I in an unthinking way, jumped in the bandwagon. It derailed my train of thought.
And yes, in times of MasterChef (a TV show in Brazil), kids cook way better than I do! In fact, I am the one that can´t be around the kitchen unsupervised, ha ha!