Per dinar, la meva germana prepara un entrepà i jo menjo un iogurt.

Yes. Per dinar is a very natural way to say for lunch in Catalan.

• per = for
• dinar = lunch / the midday meal

So Per dinar sets the context for the whole sentence: it tells you what each person is having at lunch.

In this kind of expression, Catalan often does not use an article before the meal word, so per dinar is normal.

The comma is there because Per dinar is an introductory phrase placed at the beginning of the sentence.

It works a bit like this in English:

• For lunch, my sister makes a sandwich...

The comma helps mark a small pause and separates the time/context phrase from the main sentence. In short sentences, punctuation can sometimes vary, but this comma is perfectly natural.

In Catalan, possessives are usually used with the definite article:

• la meva germana = my sister
• el meu llibre = my book

So unlike English, where you just say my sister, Catalan normally says the equivalent of the my sister.

For a learner, article + possessive + noun is the safest standard pattern to remember.

Yes, the verb already shows the subject, so jo is not strictly necessary.

Catalan often drops subject pronouns because the verb ending tells you who is doing the action:

• menjo already means I eat / I am eating

So why include jo here? Usually for contrast or emphasis:

• la meva germana prepares a sandwich
• jo eat a yogurt

It helps highlight the difference between what the sister does and what I do.

Because the two verbs have different subjects:

• la meva germana prepara = my sister prepares
• jo menjo = I eat

So the verbs are conjugated differently:

• prepara is 3rd person singular: she prepares
• menjo is 1st person singular: I eat

The infinitives are:

• preparar = to prepare
• menjar = to eat

So this sentence is giving you two different present-tense verb forms.

This is just part of how the verb menjar is written and conjugated.

The first-person singular is:

• jo menjo

Other present forms include:

• tu menges
• ell/ella menja
• nosaltres mengem

So the spelling changes a little across the forms, but this is normal. The important thing for a beginner is simply to learn menjo as the I form of menjar.

It could be either, depending on context.

The Catalan present tense can mean:

• a habit: For lunch, my sister prepares a sandwich and I eat a yogurt
• something happening now: My sister is preparing a sandwich and I’m eating a yogurt

Without extra context, both readings are possible. This is very common in Catalan.

Because both are singular masculine count nouns:

• un entrepà
• un iogurt

So Catalan uses un, the masculine singular indefinite article, just like English a/an.

Even though iogurt starts with a vowel letter, it is still masculine, so it still takes un.

A simple learner-friendly guide is:

• entrepà: roughly en-tre-PAH
  The accent mark on à shows that the last syllable is stressed.

• iogurt: roughly yo-GOORT or yo-GURT
  It begins with a y sound, similar to English yogurt.

• menjo: roughly MEN-zho
  The j in Catalan sounds like the s in measure or the g in genre, not like the English j in job.

These are only rough English approximations, but they are good enough to get started.

Not always exactly.

Entrepà usually refers to a sandwich made with a piece of bread such as a roll or baguette-style bread, often cut open and filled.

In Catalan, a sandwich made with sliced bread is often called sandvitx.

So while entrepà is often translated as sandwich, the image may be a bit different from the default English one.

Yes, Catalan word order is somewhat flexible.

This sentence starts with Per dinar to set the scene first. That is very natural. But other arrangements are also possible, depending on what you want to emphasize.

For example, you could say:

• La meva germana prepara un entrepà per dinar i jo menjo un iogurt.

Starting with Per dinar gives the sentence a nice topic frame: as for lunch...

So the original order is natural, but not the only possible one.