Μην μιλάτε όλοι μαζί, δεν καταλαβαίνω.

Because Greek uses μην for negative commands and δεν for negative statements.

• Μην μιλάτε = Don’t speak / Don’t talk
• Δεν μιλάτε = You are not speaking or You don’t speak

So in this sentence, the speaker is telling people not to do something, so μην is the correct choice.

Μιλάτε is the 2nd person plural form of μιλάω / μιλώ (to speak, to talk).

In this sentence, it is used with μην to make a negative command:

• Μην μιλάτε = Don’t talk

This same form can also be used:

• as a normal present-tense form: μιλάτε = you speak / you are speaking
• as a positive command to more than one person: Μιλάτε! = Speak!

So the context tells you how to understand it.

Grammatically, μιλάτε can be either:

• plural you = speaking to more than one person
• formal singular you = speaking politely to one person

But in this sentence, όλοι makes it clear that the speaker is addressing several people, not just one person.

Όλοι μαζί literally means all together.

In this sentence, the natural meaning is:

• all at once
• everyone at the same time

So Μην μιλάτε όλοι μαζί means Don’t all talk at once.

Όλοι is the masculine plural form of όλος (all).

Greek often uses the masculine plural when talking about:

• a mixed group of men and women
• a group whose gender is not being specified

If the speaker were talking only to women, it would be:

• Μην μιλάτε όλες μαζί

So όλοι here is the normal default for a general group of people.

Greek often leaves out subject pronouns because the verb ending already shows who is meant.

Here, μιλάτε already tells you it is you (plural/formal), and καταλαβαίνω tells you it is I.

So Greek does not need to say:

• εσείς μιλάτε
• εγώ καταλαβαίνω

unless the speaker wants extra emphasis.

Literally, it means I do not understand.

• δεν = not
• καταλαβαίνω = I understand

In this context, it naturally means something like:

• I can’t understand
• I can’t make out what is being said

So the idea is: too many people are talking at once, and the speaker cannot follow them.

Greek often leaves out an object when it is obvious from the situation.

So δεν καταλαβαίνω can simply mean:

• I don’t understand
• I can’t follow

The missing idea is understood from context: the speaker means I don’t understand what you’re saying.

If you wanted to be more explicit, you could say something like:

• Δεν σας καταλαβαίνω = I don’t understand you

But the shorter version sounds very natural here.

It can be connected to either, because μιλάω and μιλώ are two common forms of the same verb in Modern Greek.

Both mean to speak / to talk.

So learners may see:

• μιλάω
• μιλώ

and both are correct. In this sentence, μιλάτε works with either version.

A rough English-style pronunciation would be:

min mi-LA-te O-li ma-ZI, then ka-ta-la-VE-no

A few notes:

• μην sounds like min
• δ in δεν sounds like the th in this
• the stress falls on:
  • μι-ΛΑ-τε
  • μα-ΖΙ
  • καταλα-ΒΑΙ-νω in careful pronunciation, though in everyday speech it is often heard closer to kata-la-VE-no

So the whole sentence flows naturally as one warning plus one explanation: Μην μιλάτε όλοι μαζί, δεν καταλαβαίνω.