Po urodzinach babcia powiedziała, że jest naprawdę szczęśliwa.

In this sentence po means after.

• po urodzinach = after the birthday / after the birthday party
• In time expressions, po
  • a noun in the locative case is the standard way to say “after X”:
    • po obiedzie – after lunch
    • po pracy – after work
    • po szkole – after school

So po urodzinach is the natural Polish way to say “after the birthday (celebration)”.

Urodzinach is the locative case plural of urodziny (birthday).

• Nominative (dictionary form): urodziny – birthday
• Locative plural: urodzinach

The preposition po requires the locative case when it means after (in a time or space sense). That’s why we must say:

• po urodzinach (correct)
• ✗ po urodziny (incorrect)

So the form urodzinach is there because of the preposition po.

In Polish, urodziny is a plural-only noun (like scissors or trousers in English), even though in English birthday is singular.

• urodziny – birthday (always grammatically plural)
• there is no natural singular *urodzina meaning a person’s birthday in modern Polish

So you always treat urodziny grammatically as plural:

• Moje urodziny są w maju. – My birthday is in May.
  (literally: My birthdays are in May.)

The word order is not fixed; both are possible:

• Po urodzinach babcia powiedziała, że…
• Po urodzinach powiedziała babcia, że…

Both are grammatically correct.

Differences:

• Babcia powiedziała is more neutral: After the birthday, grandma said…
• powiedziała babcia slightly emphasizes who said it (grandma), similar in feel to English “…said Grandma.”

Polish word order is relatively flexible. Here, Babcia powiedziała is just the most neutral, typical version.

Both come from different verbs:

• powiedziała – past tense, perfective, from powiedzieć (to say, to tell – a single, completed act)
• mówiła – past tense, imperfective, from mówić (to speak, to talk – ongoing or repeated action)

In this sentence we describe one specific, completed statement grandma made:

• babcia powiedziała – Grandma said (once, at that moment)

If we said:

• Babcia mówiła, że jest naprawdę szczęśliwa.

it would suggest she was saying / used to say that, maybe repeatedly or over a period of time. That’s a different nuance.

This is about indirect speech.

In Polish:

• If what was said is still true at the time of speaking, we usually keep the present tense:
  • Babcia powiedziała, że jest naprawdę szczęśliwa.
    – Grandma said that she is really happy (and we assume she still is).

You can use była instead:

• Babcia powiedziała, że była naprawdę szczęśliwa.

but that suggests:

• she was happy then, at that past moment,
• and it doesn’t say anything about whether she is still happy now.

So jest focuses on her current state; była focuses on her past state.

The subject is babcia (grandma), understood from the context and from the structure powiedziała, że….

Polish often omits personal pronouns (on, ona, oni, etc.) when the subject is clear:

• Babcia powiedziała, że jest szczęśliwa.
  – literally: Grandma said that is happy.
  But we understand: that she is happy.

You could say że ona jest naprawdę szczęśliwa, but that sounds heavier and is usually unnecessary unless you want to strongly emphasize she, or contrast with someone else.

Szczęśliwa is the feminine singular form of the adjective szczęśliwy (happy).

It must agree with the (understood) subject ona / babcia, which is feminine:

• masculine: szczęśliwy
  
  • On jest szczęśliwy. – He is happy.
• feminine: szczęśliwa
  
  • Ona jest szczęśliwa. – She is happy.
  • Babcia jest szczęśliwa. – Grandma is happy.

So we say:

• Babcia powiedziała, że jest naprawdę szczęśliwa.
  not *szczęśliwy, because babcia is grammatically feminine.

Yes, you can say:

• Babcia powiedziała, że jest bardzo szczęśliwa.

But there is a nuance:

• naprawdę = really, truly (emphasizes truth / genuineness)
  
  • naprawdę szczęśliwa – really (truly) happy
• bardzo = very (emphasizes degree / intensity)
  
  • bardzo szczęśliwa – very happy

So:

• naprawdę szczęśliwa – she is genuinely happy, she really means it.
• bardzo szczęśliwa – she is very happy, strongly happy.

Both are perfectly natural; which one you choose depends on what you want to stress.

In Polish, you must put a comma before że when it introduces a subordinate clause.

Structure here:

• main clause: Po urodzinach babcia powiedziała
• conjunction: że (that)
• subordinate clause: jest naprawdę szczęśliwa

Rule:
Main clause , że + subordinate clause

So the comma is required:

• …, że jest naprawdę szczęśliwa.

In standard Polish, you cannot omit że here. You must say:

• Babcia powiedziała, że jest naprawdę szczęśliwa.

Leaving it out:

• ✗ *Babcia powiedziała jest naprawdę szczęśliwa.

is incorrect.

In fast colloquial speech, że is sometimes shortened, not fully dropped, for example to something like że’ / ż in pronunciation, but grammatically it’s still there. In writing, you keep że.

Yes, Polish allows some flexibility, but the nuances change slightly:

• jest naprawdę szczęśliwa – neutral, most common.
• naprawdę jest szczęśliwa – emphasizes naprawdę (she really is happy, maybe you doubted it).
• jest szczęśliwa naprawdę – possible, a bit more expressive/stylistic; sounds like stressing “happy, really” at the end.

All three are grammatically correct; jest naprawdę szczęśliwa is the most natural in a neutral context.