Mój brat chce się oświadczyć swojej dziewczynie, ale jeszcze nie wybrał pierścionka.

Oświadczyć się is the standard Polish verb for to propose marriage.

It is a fixed expression:

• oświadczyć się komuś = to propose to someone

So in this sentence:

• chce się oświadczyć swojej dziewczynie = he wants to propose to his girlfriend

By itself, oświadczyć usually means to declare / to state / to announce, but oświadczyć się has the special meaning to propose.

Not really. Here się is just part of the verb oświadczyć się.

In Polish, many verbs are built with się, and sometimes it does not translate neatly into English. It often looks reflexive, but in many cases it is simply part of the normal dictionary form of the verb.

So:

• oświadczyć się = to propose
• not literally to declare oneself

In this sentence, you should learn oświadczyć się as one whole unit.

Because oświadczyć się takes the dative case, not the accusative.

The pattern is:

• oświadczyć się komuś = to propose to someone

So:

• dziewczyna = base form
• dziewczynie = dative singular
• swojej also changes to match that case

That gives:

• swojej dziewczynie = to his girlfriend

If it were a direct object, you might expect the accusative, but here the person receiving the proposal is in the dative.

Because swój usually refers back to the subject of the sentence and means one’s own.

Here the subject is:

• Mój brat = my brother

So:

• swojej dziewczynie means to his own girlfriend

This is more natural in Polish than jego dziewczynie when the girlfriend belongs to the subject of the sentence.

Compare:

• swojej dziewczynie = to his own girlfriend
• jego dziewczynie = to his girlfriend, but it can sound like someone else’s girlfriend or add unnecessary emphasis

So swój is the normal choice here.

Because after a negated verb, Polish often uses the genitive instead of the accusative for the direct object.

Compare:

• wybrał pierścionek = he chose a ring
• nie wybrał pierścionka = he didn’t choose a ring

So in your sentence:

• nie wybrał pierścionka is the standard form

This is a very common rule in Polish and one that English speakers often notice early, because English does not do this.

Here jeszcze means yet.

So:

• jeszcze nie wybrał pierścionka = he hasn’t chosen a ring yet

A useful thing to remember:

• jeszcze with a negative verb often means yet
• in other contexts it can mean still or more

For example:

• Jeszcze śpi. = He’s still sleeping.
• Jeszcze nie śpi. = He isn’t sleeping yet.

This is a very common Polish structure:

• chcieć
  • infinitive = to want to do something

So:

• chce = wants
• oświadczyć się = to propose

Together:

• chce się oświadczyć = wants to propose

More literally:

• Mój brat chce się oświadczyć...
• My brother wants to propose...

Wybrał is the past tense, masculine singular form of wybrać (to choose).

It matches brat, which is masculine singular.

Compare:

• wybrał = he chose
• wybrała = she chose
• wybrało = it chose

This is an important feature of Polish: in the singular, past tense forms show gender.

Because Polish often leaves out subject pronouns when the meaning is clear from context.

In English, you usually need:

• My brother wants to propose to his girlfriend, but he hasn’t chosen a ring yet.

In Polish, once Mój brat has been introduced, the second clause can simply continue with:

• ale jeszcze nie wybrał pierścionka

You do not need on unless you want extra emphasis or contrast.

Because ale (but) is normally preceded by a comma in Polish.

So:

• ..., ale ...

This is standard punctuation. In this sentence, the comma separates two clauses:

• Mój brat chce się oświadczyć swojej dziewczynie
• ale jeszcze nie wybrał pierścionka

Sometimes, but the version here is the most natural and neutral.

In:

• chce się oświadczyć

the placement of się is normal after the finite verb chce and before the infinitive oświadczyć.

Polish się is a clitic, which means it tends to prefer certain positions and usually does not stand at the very beginning of a clause.

So for a learner, the safest choice is:

• chce się oświadczyć

rather than trying to move się around.

By itself, pierścionek means ring, especially a decorative ring.

In this sentence, because the context is a marriage proposal, it clearly means an engagement ring.

A useful contrast is:

• pierścionek = ring
• obrączka = wedding band / wedding ring

So here:

• nie wybrał pierścionka = he hasn’t chosen the engagement ring yet

Not always. Dziewczyna can mean:

• girl
• young woman
• girlfriend

The exact meaning depends on context.

Here, because of:

• swojej dziewczynie
• and the context of a marriage proposal

it clearly means girlfriend.

So in this sentence, swojej dziewczynie is best understood as to his girlfriend.