Zatímco moje maminka připravuje večeři, já myju nádobí.

Zatímco means while or whereas.

In this sentence, it introduces a clause describing one action happening at the same time as another:

• Zatímco moje maminka připravuje večeři = While my mum is preparing dinner
• já myju nádobí = I am washing the dishes

So zatímco connects the two simultaneous actions.

It can also sometimes mean whereas when contrasting two facts, but here it clearly means while.

Because zatímco moje maminka připravuje večeři is a subordinate clause, and Czech normally separates subordinate clauses from the main clause with a comma.

So the structure is:

• subordinate clause: Zatímco moje maminka připravuje večeři
• main clause: já myju nádobí

This comma is required in standard Czech.

Both are possible.

• maminka = mum / mommy
• moje maminka = my mum

Czech often leaves out possessives when the relationship is obvious from context, so Maminka připravuje večeři could also work.

Using moje makes it a little more explicit, and it can sound natural, warm, or slightly emphatic depending on context.

Not quite.

• maminka is affectionate and everyday: mum / mommy
• máma is also common and informal: mum
• matka is more formal or neutral: mother

So moje maminka sounds warm and natural in family-related speech. It is not as formal as moje matka.

Because večeře is the direct object of the verb připravovat / připravit (to prepare), so it must be in the accusative case.

The noun večeře is feminine, and its forms are:

• nominative: večeře
• accusative: večeři

So:

• večeře = dinner as the subject or dictionary form
• večeři = dinner as the thing being prepared

That is why the sentence has připravuje večeři.

Yes, but Czech often omits subject pronouns because the verb ending already shows the person.

So the more neutral version would often be:

• Zatímco moje maminka připravuje večeři, myju nádobí.

The pronoun já is included here for emphasis or contrast, something like:

• While my mum prepares dinner, I wash the dishes.
• As for me, I’m washing the dishes.

So já is not wrong at all; it just adds a little stress.

Both forms exist.

For the verb mýt (to wash), the 1st person singular present can be:

• myju
• myji

In everyday modern Czech, myju is very common and natural in speech. Myji is also correct, but it may sound a bit more formal or bookish to some learners, depending on context.

So:

• já myju nádobí = very natural spoken Czech
• já myji nádobí = also correct

Nádobí is a collective noun. Even though English says the dishes, Czech uses nádobí as a singular-looking mass noun meaning dishes / tableware / cookware in general.

So:

• myju nádobí = I’m washing the dishes

Also, nádobí has the same form in several cases, so here the accusative looks the same as the dictionary form.

This is very natural Czech; you do not need a separate plural noun here.

Yes. In Czech, the present tense of imperfective verbs often covers both:

• simple present: prepares / wash
• ongoing present: is preparing / am washing

Here the verbs are imperfective:

• připravuje from připravovat / připravovat se type meaning to be preparing
• myju from mýt in the imperfective sense to wash

Because of the context with zatímco (while), the meaning is clearly ongoing:

• While my mum is preparing dinner, I’m washing the dishes.

Czech does not need a separate progressive form like English does.

They are both present tense.

More specifically:

• připravuje = he/she is preparing
• myju = I wash / I am washing

The subjects tell you who is doing the action:

• moje maminka připravuje = my mum is preparing
• já myju = I am washing

The word order here is very natural:

• Zatímco moje maminka připravuje večeři, já myju nádobí.

Czech word order is flexible, but changes often affect emphasis rather than basic meaning.

For example, you could also say:

• Zatímco moje maminka připravuje večeři, myju nádobí.
  More neutral, without emphasis on I.

• Já myju nádobí, zatímco moje maminka připravuje večeři.
  Same meaning, but the main clause comes first.

• Nádobí myju já, zatímco moje maminka připravuje večeři.
  Strong emphasis: It’s me who washes the dishes...

So the original sentence is natural and balanced, especially if the speaker wants a little emphasis on já.

Not naturally in this context.

Zatímco can mean:

• while = two actions happen at the same time
• whereas = contrast between two facts

In this sentence, the meaning is mainly simultaneous action, so while is the best translation.

Whereas would make it sound more contrastive in English than the Czech sentence probably intends.

It is mostly neutral everyday Czech, with one slightly warm/familiar word:

• maminka is affectionate and family-style
• myju is common everyday spoken usage

So the whole sentence sounds natural in conversation or in a simple textbook example about household activities. It is not slang, and it is not especially formal either.