Mój brat nie lubi marchewki, ale lubi paprykę w sałatce.

Because mój has to agree with brat in gender, number, and case.

• brat = brother
• It is masculine singular
• In the nominative case, the matching form of my is mój

So:

• mój brat = my brother
• moja would be for a feminine noun, for example moja siostra = my sister
• moje would be for a neuter noun, for example moje dziecko = my child

Polish often drops subject pronouns when they are not needed.

In English, you usually say He likes... or My brother likes...
In Polish, once the subject is clear, you normally do not add on (he) unless you want extra emphasis or contrast.

Here, mój brat already tells us who the subject is, so there is no need to say:

• Mój brat on nie lubi... — this would sound unnecessary in a neutral sentence

Polish is a pro-drop language, so leaving out pronouns is very common.

Lubi is the 3rd person singular form of the verb lubić (to like).

The subject is mój brat = my brother, which is he, so the verb must match he/she/it:

• ja lubię = I like
• ty lubisz = you like
• on/ona/ono lubi = he/she/it likes

So:

• Mój brat lubi... = My brother likes...
• Mój brat nie lubi... = My brother does not like...

This is one of the most important grammar points in the sentence.

Both marchewka and papryka are feminine nouns, and with a positive verb like lubi they would normally take the accusative singular:

• lubi marchewkę
• lubi paprykę

But after negation in Polish, the direct object often changes to the genitive.

So:

• lubi paprykę = accusative, because the verb is affirmative
• nie lubi marchewki = genitive, because the verb is negated

That is why the endings are different:

• marchewka → marchewki after nie lubi
• papryka → paprykę after lubi

Here it is singular.

That can be confusing, because marchewki can also be a plural form in other contexts. But in this sentence, it is the genitive singular of marchewka.

Why we know it is singular here:

• The sentence is talking about carrot as a food/item in general
• It follows nie lubi, which commonly takes the genitive singular with an uncounted/general object

So here:

• marchewki = carrot / carrots in the general food sense, but grammatically it is genitive singular

Because the preposition w often requires the locative case when it means in or inside.

The basic noun is:

• sałatka = salad

After w, it becomes:

• w sałatce = in the salad / in salad

This is the locative singular form.

So the pattern is:

• sałatka → w sałatce
• książka → w książce
• szafka → w szafce

This -ce ending is very common for feminine nouns ending in -ka.

It means in a salad or as part of a salad.

So the idea is not just that the brother likes peppers in general, but that he likes them when they are in salad.

In English, depending on context, you might translate it as:

• ...but he likes pepper in salad
• ...but he likes peppers in a salad
• ...but he likes bell pepper in salads

The Polish phrase w sałatce gives the context in which he likes the pepper.

In practice, it goes with the second part: lubi paprykę w sałatce.

That means the natural interpretation is:

• He likes papryka in salad

So yes, it is closely connected to paprykę, but in grammatical terms it also tells you the context of liking.

A native speaker would naturally understand:

• He does not like carrot,
• but he does like pepper when it is in a salad.

Repeating lubi is the most neutral and natural choice here.

• Mój brat nie lubi marchewki, ale lubi paprykę w sałatce.

This is clear and balanced:

• doesn’t like X
• but likes Y

Polish can sometimes omit repeated material, but here repeating the verb sounds best in ordinary speech and writing.

A more compressed or contrastive version is possible, for example:

• Mój brat nie lubi marchewki, ale paprykę lubi w sałatce.

But that sounds more marked and puts extra emphasis on paprykę.

So for a learner, the repeated lubi is the normal pattern to use.

Because in Polish, ale (but) normally takes a comma before it.

This is standard punctuation:

• ..., ale ...

So:

• Mój brat nie lubi marchewki, ale lubi paprykę w sałatce.

This is similar to English, where a comma often appears before but when it joins two clauses.

Because Polish has no articles.

English distinguishes between:

• a salad
• the salad

Polish usually does not mark that difference with a separate word. The listener understands it from context.

So:

• w sałatce could mean in a salad or in the salad, depending on the situation

This is completely normal in Polish.

Yes. Polish word order is more flexible than English word order.

The sentence as given is neutral and natural:

• Mój brat nie lubi marchewki, ale lubi paprykę w sałatce.

But Polish can move things around for emphasis or contrast. For example:

• Paprykę mój brat lubi w sałatce, ale marchewki nie lubi.

That version is more emphatic and contrastive.

Even though word order can change, the original sentence is a good standard model because it is:

• clear
• natural
• easy to understand

In Polish, papryka usually means pepper, especially bell pepper as a vegetable.

It does not usually mean the powdered spice paprika in this kind of sentence.

So in this context:

• paprykę w sałatce most naturally means bell pepper in salad

English can be tricky here because pepper may mean different things. For most learners, the safest interpretation is:

• bell pepper

A few useful pronunciation notes:

• mój sounds roughly like mooy
• brat has a short a, like braht
• lubi = LOO-bee
• marchewki = roughly mar-HEV-kee
  
  • ch sounds like a strong h
• paprykę = roughly pa-PRI-keng
  
  • the final ę is a nasal vowel
• sałatce = roughly sa-WAT-tseh

Also, Polish stress is usually on the second-to-last syllable:

• marCHEWki
• paPRYkę
• saŁATce

The letter ł sounds like English w, so sałatce begins more like sa-wat-... than sa-lat-...