Tata mówi, że jeden tost to za mało, więc robi sobie jeszcze drugi.

Tata means dad and is much more natural in everyday speech. Ojciec means father and sounds more formal, neutral, or sometimes emotionally distant.

So:

• Tata mówi... = Dad says...
• Ojciec mówi... = Father says...

In normal family conversation, tata is what you would expect.

Polish often leaves out subject pronouns when the verb already makes the subject clear.

Here:

• mówi = (he) says
• robi = (he) makes / is making

Because the sentence already begins with Tata, there is no need to repeat on (he). Using on here would usually sound unnecessary unless you wanted extra emphasis.

Yes, tost alone would be possible in some contexts, but jeden tost specifically emphasizes one toast.

Compare:

• Tost to za mało = Toast is too little / one piece of toast is not enough
• Jeden tost to za mało = One toast is too little

Using jeden makes the quantity explicit. It matches the idea that he then makes a second one.

Here to links two parts of the sentence, a bit like is in English.

So:

• Jeden tost to za mało = One toast is too little

This structure is very common in Polish:

• To jest trudne = This is difficult
• Kawa to mój ulubiony napój = Coffee is my favorite drink
• Jeden tost to za mało = One toast is too little

In casual Polish, to often works as the main linker in this kind of sentence, even without jest.

Yes, you can, but jeden tost to za mało sounds more natural here.

Very roughly:

• jeden tost to za mało = the most idiomatic, conversational version
• jeden tost jest za mało = grammatically understandable, but a bit less natural in this kind of statement

Polish often prefers the X to Y pattern in definitions, evaluations, and general statements.

Za mało means too little / not enough.

• mało = little / not much
• za mało = too little

So:

• Jeden tost to mało = One toast is little / One toast is not much
• Jeden tost to za mało = One toast is too little / not enough

The word za often adds the meaning of too:

• za drogo = too expensive
• za późno = too late
• za mało = too little

Że means that.

So:

• Tata mówi, że... = Dad says that...

Just like in English, Polish often uses that after verbs like say, think, know, etc.

Examples:

• Mówię, że to prawda. = I’m saying that it’s true.
• Myślę, że masz rację. = I think that you’re right.

In English, that is often omitted. In Polish, że is normally kept.

Because Polish punctuation usually separates clauses more consistently than English.

Here you have:

• Tata mówi, że... — a main clause plus a subordinate clause, so a comma goes before że
• ..., więc robi sobie jeszcze drugi. — another clause introduced by więc, so a comma goes before więc

So the commas are standard and expected in Polish.

Więc means so, therefore, or thus.

In this sentence:

• ..., więc robi sobie jeszcze drugi. = ..., so he makes himself another/second one.

It introduces a result or consequence:

• one toast is not enough,
• so he makes another one.

Sobie adds the idea that he is doing it for himself.

So:

• robi drugi = he makes a second one
• robi sobie drugi = he makes himself a second one

This is very common in Polish when someone prepares food, drink, or something for their own use:

• Zrobiłem sobie kawę. = I made myself a coffee.
• Kupili sobie dom. = They bought themselves a house.
• Usmażył sobie jajka. = He fried himself some eggs.

Without sobie, the sentence is still possible, but sobie makes it sound more natural and personal here.

Sobie is the dative form of siebie (oneself / self), used here in a reflexive sense.

In simpler terms, it means something like:

• for himself
• to himself

In this sentence, sobie refers back to Tata.

So robi sobie literally has the sense of makes for himself.

Here jeszcze drugi means another one, literally a second one.

• drugi = second
• jeszcze drugi = yet another / one more / a second one

Because he already has one toast, making drugi means making a second. In natural English, that is often translated as another one.

Because drugi agrees with an implied noun: tost.

The full idea is:

• robi sobie jeszcze drugi tost

The noun tost is masculine inanimate. In the singular accusative, masculine inanimate nouns usually look like the nominative. That is why you get:

• drugi tost
  not
• drugiego tosta

So even though drugi is the object of robi, its form stays drugi because masculine inanimate accusative = nominative here.

Because Polish, like English, often leaves out a noun when it is obvious from context.

Compare in English:

• One toast is not enough, so he makes another.

You do not have to repeat toast. Polish works the same way:

• ...robi sobie jeszcze drugi
  literally: ...makes himself one more second one
• understood meaning: ...makes himself another toast

The omitted noun is easy to recover from the earlier part of the sentence.

Not completely. Polish word order is flexible, but this version sounds natural and neutral.

• robi sobie jeszcze drugi = natural
• robi jeszcze drugi sobie = possible only in special emphasis, but not natural here
• jeszcze robi sobie drugi = possible in a different rhythm or emphasis

The sentence puts the elements in a smooth everyday order:

1. verb: robi
2. reflexive/dative pronoun: sobie
3. adverb: jeszcze
4. object: drugi

That is a very typical conversational pattern.