Мне приятно, когда мы понимаем друг друга.

Because Russian often uses an impersonal construction for feelings and reactions.

Мне приятно literally means something like To me, it is pleasant.
So the person experiencing the feeling is put in the dative case:

• я = I
• мне = to me

This same pattern is very common in Russian:

• Мне холодно = I am cold
• Мне грустно = I am sad
• Мне интересно = I am interested / It is interesting to me

So мне приятно is a very natural Russian way to say I’m pleased / I find it nice.

Here приятно means pleasant, nice, or pleasing in the sense of it feels good or I’m pleased.

In this sentence, Мне приятно, когда... means:

• I like it when...
• It makes me happy when...
• I’m pleased when...

So it is not just a cold dictionary meaning like pleasant. In real use, it often expresses a warm emotional reaction.

In this sentence, приятно is being used as a predicative state word—the kind of word Russian often uses in impersonal sentences.

For a learner, the easiest way to think about it is:

• it does not describe a noun
• it acts as the main predicate
• it expresses a state or feeling

So in Мне приятно, приятно is the core idea: it feels pleasant.

This is why it does not change for gender or number here.

Because когда мы понимаем друг друга is a subordinate clause.

Russian normally puts a comma before subordinate clauses introduced by words like:

• когда = when
• если = if
• что = that
• потому что = because

So:

• Мне приятно, когда мы понимаем друг друга.

The comma is required because the second part explains when the feeling happens.

Because когда means when or whenever, while если means if.

The sentence is talking about a situation that the speaker experiences as real or recurring:

• Мне приятно, когда мы понимаем друг друга.
  = I’m pleased when / whenever we understand each other.

If you used если, it would sound more conditional:

• Мне будет приятно, если мы поймём друг друга.
  = I’ll be pleased if we understand each other.

So когда fits better for a general emotional reaction.

Because Russian present tense is often used for a general truth, a habitual situation, or something that happens whenever the situation comes up.

So когда мы понимаем друг друга means:

• when we understand each other
• when we are understanding each other
• whenever we understand each other

It does not have to mean only this exact moment.

If you wanted a past meaning, you would change the verb:

• когда мы понимали друг друга = when we understood each other / used to understand each other
• когда мы поняли друг друга = when we came to understand each other

Друг друга means each other.

So:

• мы понимаем друг друга = we understand each other

This is a special Russian reciprocal expression. The form changes depending on the case needed by the verb.

Here, the verb понимать takes a direct object, so друг друга is in the form used for that role.

You will also see other forms:

• друг другу = each other, to each other
• друг с другом = with each other
• друг о друге = about each other

So it is best to learn друг друга as the standard way to say each other, while remembering that the second word changes with case.

Because Russian usually says explicitly understand each other with друг друга.

If you only say мы понимаем, that usually means we understand something in general, but it does not clearly express the reciprocal idea.

Compare:

• Мы понимаем русский. = We understand Russian.
• Мы понимаем друг друга. = We understand each other.

So друг друга is necessary here.

Yes, it could be omitted, because the verb ending -ем already shows we:

• когда понимаем друг друга

That said, Russian often keeps the pronoun for clarity, emphasis, or natural flow:

• когда мы понимаем друг друга

Including мы sounds completely normal. It may feel a little more explicit than leaving it out.

Yes. Russian word order is fairly flexible.

You could also say:

• Когда мы понимаем друг друга, мне приятно.

Both versions are correct. The difference is mostly about emphasis:

• Мне приятно, когда мы понимаем друг друга.
  Focus first on my feeling
• Когда мы понимаем друг друга, мне приятно.
  Focus first on the situation

So the original sentence is natural, but not the only possible order.

Yes, you could, but the nuance is a little different.

• Мне приятно... = It feels nice to me / I’m pleased
• Я рад / рада... = I’m glad / happy

A few differences:

1. Я рад / рада agrees with the speaker’s gender:

   • рад if the speaker is male
   • рада if the speaker is female

2. Мне приятно is gender-neutral and often sounds a bit softer or more understated.

So both are natural, but мне приятно is a very common and elegant way to express this feeling.

A simple pronunciation guide is:

Mne priyátna? No—careful: the correct word is priyátno.
So the full sentence is approximately:

Mnye priyátna? Again, better to give the full phrase correctly:

Mne priyátna, kagdá my panimáyem drug drúga would be wrong because приятно ends in -no, not -na.

A better approximate pronunciation is:

Mnye priyátna? Still not right.

The sentence is approximately:

Mne priyátna? No.

Let’s give it cleanly:

Mne priyátno, kogdá my panimáyem drug drúga.

Main stress:

• мне
• приятно → stress on я: прия́тно
• когда → stress on last syllable: когда́
• понимаем → stress on ма: понима́ем
• друга → stress on дру: дру́га

The combination друг друга is pronounced smoothly together in normal speech.