Teniu taronges? No, no en tenim, però tenim suc.

Catalan does not use an auxiliary like English do to form ordinary questions.

So:

• Teniu taronges? = literally something like Have you oranges?
• natural English meaning = Do you have oranges?

Catalan usually forms this kind of question with:

• the normal verb form
• intonation in speech
• question marks in writing

The same is true for negatives:

• No en tenim = We don’t have any

There is no extra verb equivalent to English do here.

Teniu is the present tense, 2nd person plural form of tenir (to have).

So it means:

• you all have
• or in a question, do you all have...?

A quick pattern:

• jo tinc = I have
• tu tens = you have (singular, informal)
• ell/ella té = he/she has
• nosaltres tenim = we have
• vosaltres teniu = you all have
• ells/elles tenen = they have

So Teniu taronges? is addressed to more than one person, or to a group collectively.

Because the point of view changes.

• Teniu taronges? = Do you have oranges?
• No, no en tenim = No, we don’t have any

The question is addressed to you, but the person answering speaks about we.

So:

• teniu = you all have
• tenim = we have

This is completely natural, just like in English:

• Do you have oranges?
• No, we don’t, but we have juice.

The first No is a standalone reply:

• No = No

The second no is the normal negative word inside the full sentence:

• no en tenim = we don’t have any

So the whole thing is basically:

• No. We don’t have any.

It is written with a comma here, but functionally it is the same idea: a short answer followed by a full negative sentence.

En is a very common Catalan pronoun. Here it replaces taronges so you do not have to repeat the noun.

So:

• Teniu taronges?
• No, no en tenim.

means:

• Do you have oranges?
• No, we don’t have any.

You can think of en here as something like:

• any
• of them
• of it

depending on the context.

It is especially common with:

• plural indefinite nouns
• mass nouns
• food and drink
• quantities

More examples:

• Teniu pa? Sí, en tenim. = Do you have bread? Yes, we have some.
• Vols cafè? No en vull. = Do you want coffee? I don’t want any.

For English speakers, this is one of the most important uses of en.

Yes, absolutely.

Both are correct:

• No, no en tenim.
• No, no tenim taronges.

The difference is mainly that:

• no en tenim avoids repeating taronges
• no tenim taronges repeats the noun explicitly

In Catalan, using en is often the more natural choice when the noun was just mentioned.

So if someone has already asked about oranges, No, no en tenim sounds very normal.

Because both nouns are being used in a general / indefinite sense.

• Teniu taronges? = Do you have oranges / any oranges?
• Tenim suc = We have juice / some juice

This is not about specific, already identified oranges or a specific juice.

Compare:

• Teniu taronges? = Do you have oranges?
• Teniu les taronges? = Do you have the oranges?

And:

• Tenim suc = We have juice
• Tenim el suc = We have the juice

So the lack of article here is normal and matches the indefinite meaning.

Because en is only used to replace something already mentioned or understood.

In the sentence:

• No, no en tenim, però tenim suc.

en refers back to taronges. But suc is new information, so it is said normally:

• tenim suc = we have juice

If the conversation had already been about juice, then en could be used:

• Teniu suc? Sí, en tenim. = Do you have juice? Yes, we have some.

So in your sentence:

• en = replaces taronges
• suc = new noun, so it is stated directly

Però means but.

It introduces a contrast:

• No, no en tenim = we don’t have any oranges
• però tenim suc = but we do have juice

So the idea is:

• no oranges
• but juice is available

Also, the accent in però shows the stressed vowel and helps distinguish its spelling.