He fet una foto de la taula abans de sopar.

In Catalan, he here does not mean the English pronoun he. It is the first-person singular form of haver used as an auxiliary verb.

So:

• he = I have
• he fet = I have done / I have made

Catalan usually leaves out the subject pronoun jo, so Jo he fet... is grammatical, but He fet... is the normal unmarked way to say it.

Because fet is the past participle of fer.

• fer = to do / to make
• fet = done / made

Catalan forms the present perfect with:

• haver
  • past participle

So:

• he fet = I have done / made
• not he fer

This is similar to English I have made, not I have make.

Because Catalan uses a different idiom. The normal expression is:

• fer una foto = to take a photo

Even though fer usually means to do or to make, with foto it is the standard everyday verb. Languages often package actions differently, and this is one of those cases where a word-for-word translation from English does not work.

Yes, foto is feminine:

• una foto
• la foto

This is because foto is a shortened form of fotografia, which is feminine. So even though many nouns ending in -o are masculine, foto is a feminine exception.

Here de links the photo to what appears in it:

• una foto de la taula = a photo of the table

So de la taula tells you what the photo is of.

This use of de is very common in Catalan after nouns like foto, imatge, record, olor, etc.

Because in Catalan, de + la stays de la.

Some prepositions do contract with articles, for example:

• de + el = del
• a + el = al

But:

• de + la = de la
• a + la = a la

So de la taula is exactly what you should expect.

Not if you mean a photo of the table.

The natural expression for what appears in the photo is:

• una foto de la taula

Using a la taula would suggest a different relationship, such as location or direction, not the thing represented in the picture. So for photo of X, Catalan normally uses de.

Here sopar is most naturally understood as an infinitive verb:

• abans de sopar = before having dinner / before eating dinner

Catalan commonly uses:

• abans de + infinitive

Examples:

• abans de marxar = before leaving
• abans de dormir = before sleeping
• abans de sopar = before having dinner

Since sopar can also be a noun meaning dinner/supper, English may translate it simply as before dinner, but grammatically in this sentence it is most naturally read as an infinitive.

Because sopar is functioning as a verb infinitive here, not as a specific noun.

• abans de sopar = before having dinner
• abans del sopar = before the dinner / before the meal / before the dinner event

So the absence of the article helps show that this is a general action, not a specific named dinner.

Often yes, depending on context and regional usage.

• he fet = present perfect
• vaig fer = periphrastic past, a very common Catalan past tense

Very roughly:

• he fet often has a link to the present or can sound more like I have taken
• vaig fer often sounds more like I took

In many real-life situations, both are possible, but they are not always identical in nuance. A learner should recognize both as very common ways to talk about past actions.

Because Catalan is a pro-drop language: the verb ending often already tells you who the subject is.

• he fet already means I have done/made
• so jo is not necessary

You can add jo for emphasis or contrast:

• Jo he fet una foto, no ell.
  I took a photo, not him.

But in a neutral sentence, leaving it out is more natural.

Yes. Catalan word order is flexible, especially with time expressions.

You can say:

• He fet una foto de la taula abans de sopar.
• Abans de sopar, he fet una foto de la taula.

Both are grammatical. The second version gives a little more prominence to the time phrase.