Mesmo sem maionese, o Pedro come sempre pepino na sandes.

Mesmo sem means even without.

• sem maionese = without mayonnaise
• mesmo sem maionese = even without mayonnaise

The word mesmo adds emphasis. It suggests something like: despite not having mayonnaise, the statement is still true.

If you said just Sem maionese, o Pedro..., that would still be understandable, but mesmo makes the contrast stronger.

In European Portuguese, it is very common to use the definite article before a person's name:

• o Pedro
• a Maria

This does not translate literally as the Pedro in natural English. It is just a normal feature of Portuguese, especially in Portugal.

In some contexts, leaving the article out is possible, but in everyday European Portuguese, o Pedro sounds very natural.

Come is the 3rd person singular present tense of the verb comer (to eat).

So:

• eu como = I eat
• tu comes = you eat
• ele / ela come = he / she eats

Here, o Pedro come means Pedro eats.

Because the sentence also has sempre (always), the present tense expresses a habitual action:

• o Pedro come sempre... = Pedro always eats...

Yes, sempre can move, but o Pedro come sempre pepino na sandes is a very natural order.

Portuguese adverbs often have some flexibility. For example:

• O Pedro come sempre pepino na sandes.
• O Pedro sempre come pepino na sandes.

Both are possible. The version with come sempre sounds very natural and neutral here.

So the main point is: the adverb position is flexible, but this sentence uses a common everyday order.

Here, pepino is being used in a general sense, as an ingredient or food item, not as a specific individual cucumber.

So Portuguese naturally says:

• come pepino = eats cucumber

rather than:

• come o pepino = eats the cucumber

Using no article here is similar to English when talking about food in general:

• He eats cucumber in his sandwich.

If you used o pepino, it would usually sound like you mean a specific cucumber already identified in the context.

Na is a contraction of:

• em
  • a = na

So:

• na sandes = in the sandwich

Because sandes is feminine singular (a sandes), the contraction is na.

Compare:

• no pão = em + o
• na sandes = em + a

In English, we might sometimes say in the sandwich or on the sandwich, but in Portuguese na sandes is a normal way to refer to something inside the sandwich.

Yes, this is very much a European Portuguese word.

In Portugal, sandes is a common word for sandwich, and it is feminine:

• a sandes
• na sandes

A learner who knows Brazilian Portuguese may expect o sanduíche, which is much more common in Brazil.

So for Portugal:

• a sandes = very natural

Normally, pepino means cucumber.

That is the default meaning.

If you want to say pickle in Portuguese, that is usually expressed differently, for example with picles or a more specific phrase depending on context.

So in this sentence, a learner should understand pepino as cucumber, not pickles.

Portuguese often leaves out a possessive when it is clear from the context.

So na sandes can be understood as:

• in the sandwich
• and, depending on context, effectively in his sandwich

If you want to make the possession explicit, you could say:

• na sua sandes
• na sandes dele

But Portuguese does not always need to state his or her as often as English does.

Also, sua can sometimes be ambiguous, so dele may be clearer if needed.

It is very normal and appropriate here.

Mesmo sem maionese is an introductory phrase placed before the main clause, so the comma helps separate it from the rest of the sentence:

• Mesmo sem maionese, o Pedro come sempre pepino na sandes.

That punctuation makes the sentence easier to read and reflects the pause you would often hear in speech.

In very short sentences, commas after fronted phrases are sometimes omitted, but here the comma is a good standard choice.

Yes. Portuguese allows that.

For example:

• O Pedro come sempre pepino na sandes, mesmo sem maionese.

This still works, but the emphasis changes slightly.

• At the beginning: Mesmo sem maionese... gives that idea immediate prominence.
• At the end: the sentence first states the fact, then adds the contrasting detail.

So both are possible, but the original version highlights the even without mayonnaise idea more strongly.