El paquet és petit, però la bústia del carrer també és petita.

Because adjectives in Catalan usually agree with the noun they describe in gender and number.

• paquet is masculine singular → petit
• bústia is feminine singular → petita

This is very common in Catalan:

• un cotxe petit = a small car
• una casa petita = a small house

So the adjective changes form depending on the noun.

del carrer means of the street or more naturally in English, on the street / in the street depending on context.

It is made of:

• de = of/from
• el carrer = the street

So:

• de + el = del

This contraction is required in normal Catalan.

In this sentence, la bústia del carrer means something like the mailbox/postbox on the street or the street mailbox.

Because Catalan normally contracts de + el into del.

So:

• de + el → del
• a + el → al

Examples:

• la porta del cotxe = the door of the car
• vaig al mercat = I go to the market

So la bústia del carrer is the correct form, not de el carrer.

també means also or too.

Here it shows that the second part of the sentence adds similar information:

• El paquet és petit = The package is small
• però la bústia del carrer també és petita = but the street mailbox is also small

So the idea is: the package is small, but the mailbox is small too, which explains the problem or contrast.

Catalan usually repeats the verb where English also would:

• El paquet és petit
• la bústia del carrer també és petita

The verb és is the 3rd person singular form of ser = to be.

Even though the two clauses are connected by però (but), Catalan still normally states the verb again in the second clause.

In Catalan, adjectives often come after the noun, especially when they describe a basic quality like size, color, shape, etc.

So:

• paquet petit = small package
• bústia petita = small mailbox

This is more typical in Catalan than English, where adjectives usually come before the noun.

That said, adjective placement in Catalan can sometimes vary for style or meaning, but in this sentence the normal order is noun + adjective.

però means but.

It introduces a contrast between the two ideas:

• the package is small
• but the mailbox is also small

So even though the package is not big, the mailbox is still too small for it.

Also, the accent in però helps distinguish pronunciation and spelling.

el and la are the definite articles in Catalan, meaning the.

• el paquet = the package
• la bústia = the mailbox

Catalan uses articles very regularly, and each one agrees with the gender of the noun:

• el for masculine singular
• la for feminine singular

This is something English speakers need to get used to, since English the does not change.

In Catalan, every noun has grammatical gender, and you usually learn it together with the word.

Here:

• el paquet → masculine
• la bústia → feminine

Sometimes the ending gives you a clue:

• nouns ending in -a are often feminine, like bústia
• but this is not a perfect rule, so it is best to learn nouns with their article:
  • el paquet
  • la bústia

That makes it much easier to choose the correct adjective form later.

The accent marks help show stress and sometimes distinguish words.

A few useful points here:

• és = is
  The accent distinguishes it from es, which can be a pronoun.
• però = but
• també = also
• bústia = mailbox

For a learner, the most important thing is:

• keep the accents when writing
• try to stress the syllable indicated by the accent

Accent marks are an important part of correct Catalan spelling.

Yes. bústia can often be translated as:

• mailbox
• postbox
• sometimes letter box

The best English translation depends on context and regional variety of English.

In this sentence, la bústia del carrer most likely refers to a public mailbox/postbox in the street, not the private mailbox attached to a house or apartment.

Yes. A comma before però is very normal when it connects two full clauses, just like a comma before but in English.

Here the sentence has two parts:

• El paquet és petit
• però la bústia del carrer també és petita

So the comma helps separate the contrast clearly.

Yes, it could, but the meaning would be slightly less explicit.

• El paquet és petit, però la bústia del carrer és petita.
• El paquet és petit, però la bústia del carrer també és petita.

With també, the sentence emphasizes that the second thing shares the same quality: smallness.

So també makes the relationship between the two clauses clearer: the package is small, and the mailbox is also small.