Bağış kutusu boş kalmadı; bilakis hızla doldu.

Because bağış kutusu is a Turkish noun compound, literally something like donation box / box for donations.

In this kind of compound, the second noun usually takes the 3rd person possessive ending:

• kutu = box
• kutu-su = its box / box of

So:

• bağış kutusu = donation box
• similar patterns:
  • çay bardağı = tea glass
  • otobüs durağı = bus stop
  • okul kapısı = school gate

Even though English does not show this extra ending, Turkish normally does in compounds like this.

The -su is the compound/possessive ending attached to kutu.

The base word is:

• kutu = box

With the ending:

• kutu-su

The form is -sı / -si / -su / -sü depending on vowel harmony. Here it becomes -su because the last vowel in kutu is u.

The buffer consonant s appears because the noun ends in a vowel.

So:

• kutu + su → kutusu

This is a very natural Turkish choice.

• boş olmak = to be empty
• boş kalmak = to remain empty / stay empty

Here the idea is not just it was not empty, but more specifically it did not remain empty.

So:

• boş olmadı would sound more like it wasn’t empty
• boş kalmadı means it didn’t stay empty / it didn’t remain empty

That fits especially well because the second half says it quickly filled up.

Kalmak often means to stay, remain, be left.

In this sentence:

• boş kalmadı

it combines with the adjective boş to mean:

• did not remain empty

This is a very common pattern in Turkish:

• açık kaldı = it stayed open
• kapalı kalmadı = it did not remain closed
• yalnız kalmak = to remain alone

So kalmak helps express a continuing state.

Both are in the simple past (also called the definite past in Turkish).

Breakdown:

• kal-ma-dı

  • kal- = remain/stay
  • -ma- = negation
  • -dı = past

• dol-du

  • dol- = fill up / become full
  • -du = past

So both verbs describe completed events in the past.

Because Turkish usually forms verbal negation by inserting -ma / -me before the tense ending.

So:

• kaldı = it remained
• kalmadı = it did not remain

Pattern:

• verb stem + negative + tense/person

More examples:

• geldi = he/she came
• gelmedi = he/she did not come

So kal-ma-dı is completely regular.

Bilakis means on the contrary, quite the opposite, or far from that.

It is correct and elegant, but it sounds a bit more formal or literary than some everyday alternatives.

Common alternatives:

• aksine = on the contrary
• hatta tam tersine = in fact, quite the opposite

So the sentence has a slightly polished tone because of bilakis.

The semicolon separates two closely related clauses:

• Bağış kutusu boş kalmadı
• bilakis hızla doldu

It works a lot like English punctuation in a sentence such as:

• It did not remain empty; on the contrary, it filled quickly.

A comma could also appear in some contexts, but the semicolon gives the contrast a stronger pause and makes the sentence feel more formal and well-structured.

Hızla means quickly / rapidly / with speed.

It comes from:

• hız = speed

and the ending:

• -la / -le

This ending can sometimes mean with or can turn a noun into an adverbial expression.

So:

• hızla = with speed → quickly

Similar examples:

• dikkatle = carefully
• sessizce is another adverb form, but with a different ending
• öfkeyle = angrily / with anger

Because dolmak and doldurmak are different verbs.

• dolmak = to become full / fill up
• doldurmak = to fill something

In this sentence, the box itself is the subject, so Turkish uses dolmak:

• Kutusu doldu = The box filled up / became full

If a person were doing the action, you would use doldurmak:

• Birisi bağış kutusunu doldurdu = Someone filled the donation box

So doldu is the correct intransitive verb here.

Yes, Turkish often leaves subject pronouns unstated when they are clear from context.

Here the subject is explicitly the noun phrase:

• Bağış kutusu

So there is no need to add o.

In fact, saying:

• Bağış kutusu ... o ...

would usually be unnecessary and awkward unless you were emphasizing something.

The word order is quite natural and effective.

First clause:

• Bağış kutusu boş kalmadı
  • subject first
  • adjective + verb phrase
  • verb at the end, as is typical in Turkish

Second clause:

• bilakis hızla doldu
  • contrast word first for emphasis
  • adverb before the verb
  • verb again at the end

Turkish is flexible with word order, but this version sounds smooth and emphasizes the contrast nicely:

• not empty,
• quite the opposite,
• it filled quickly.

Yes, very naturally.

For example:

• Bağış kutusu boş kalmadı; aksine hızla doldu.

This means almost the same thing.

Very roughly:

• bilakis can feel a bit more formal, rhetorical, or literary
• aksine is also standard and often sounds a little more neutral in modern usage

Both are correct here.

Because bağış kutusu is the subject of the sentence, not the direct object.

The accusative in Turkish is used for specific direct objects:

• Bağış kutusunu gördüm = I saw the donation box

But here:

• Bağış kutusu ... doldu
• Bağış kutusu ... kalmadı

the box is the thing doing/undergoing the state change as the subject, so no accusative is needed.