Jej siostra jest programistką, ale wcześniej chciała być tłumaczką.

Jej means her. So jej siostra means her sister.

• jej = her
• jego = his
• swoja / swoją / swoje = reflexive one’s own, used in different situations

Here, the sentence is simply talking about her sister, so jej is the natural choice.

Also note that jej does not change its form here, unlike many other Polish pronouns.

After być (to be) in Polish, when you say what someone is or becomes / wants to be, the noun is very often put in the instrumental case.

So:

• programistka → programistką
• tłumaczka → tłumaczką

That is why the sentence has:

• jest programistką = she is a programmer
• chciała być tłumaczką = she wanted to be a translator

This is one of the most important patterns to learn in Polish:

• X is a Y → X jest Y-em / Y-ą
• X wants to be a Y → X chce być Y-em / Y-ą

They are in the instrumental singular.

For many feminine nouns ending in -ka, the instrumental singular ends in -ką:

• nauczycielka → nauczycielką
• studentka → studentką
• tłumaczka → tłumaczką
• programistka → programistką

So this sentence is a good example of the instrumental being used after jest and być.

Because the subject is feminine.

The sentence is about siostra (sister), which is feminine, so the past tense verb must also be feminine:

• chciała = she wanted
• chciał = he wanted

In Polish past tense, the verb agrees with gender:

• on chciał = he wanted
• ona chciała = she wanted
• ono chciało = it wanted

Because in Polish, the subject pronoun is often omitted if it is already clear from context.

Here, siostra is the subject, so you do not need to repeat ona:

• Jej siostra jest programistką, ale wcześniej chciała być tłumaczką.

This is completely natural in Polish.

You could say ona chciała, but it would usually be unnecessary unless you want emphasis or contrast.

Wcześniej means earlier / previously / before that.

In this sentence, it tells us that in the past, before the present situation, she wanted something different:

• now: she is a programmer
• earlier: she wanted to be a translator

So ale wcześniej is like:

• but earlier
• but previously
• but before that

Ale means but.

It connects two contrasting ideas:

• Jej siostra jest programistką = Her sister is a programmer
• ale wcześniej chciała być tłumaczką = but earlier she wanted to be a translator

So the contrast is between:

• what she is now
• what she wanted before

Yes. Programistką comes from the feminine noun programistka.

The masculine form is:

• programista = male programmer

Their instrumental forms are:

• programista → programistą
• programistka → programistką

Likewise:

• tłumacz = male translator
• tłumaczka = female translator

So this sentence clearly refers to a woman.

Because both nouns are feminine and are being put into the instrumental singular.

The nominative forms are:

• programistka
• tłumaczka

In the instrumental singular, feminine nouns of this type usually change to -ką:

• -ka → -ką
• -czka also becomes a form ending in -ką, so tłumaczka → tłumaczką

The exact spelling of the stem may look a little different, but the important pattern is that the feminine instrumental often ends in -ą, and for many nouns in -ka it becomes -ką.

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

For example, these are all possible:

• Jej siostra jest programistką, ale wcześniej chciała być tłumaczką.
• Jej siostra jest programistką, ale chciała wcześniej być tłumaczką.
• Wcześniej jej siostra chciała być tłumaczką, ale jest programistką.

But the original version sounds very natural and clear. Placing wcześniej after ale neatly emphasizes the contrast with the present.

Not here. You need być because the meaning is wanted to be.

• chciała być tłumaczką = she wanted to be a translator

If you removed być, the sentence would be incorrect:

• chciała tłumaczką ❌

So the structure is:

• chcieć + infinitive
• here, the infinitive is być

Because ale introduces another clause, and in Polish it is normally preceded by a comma.

So:

• Jej siostra jest programistką, ale wcześniej chciała być tłumaczką.

This is standard Polish punctuation, just like English usually puts a comma before but when joining two full clauses.

It contains both.

• jest = present tense, is
• chciała = past tense, wanted

So the sentence compares:

• her current profession
• her earlier wish

That mixture of tenses is exactly what gives the sentence its meaning.