Paul va dormir ; je dis bonne nuit.

Va dormir is the near future construction: aller + infinitive.

• Paul dort = Paul is sleeping / Paul sleeps
• Paul va dormir = Paul is going to sleep

So va dormir focuses on what is about to happen, not what is happening already.

After aller when it is used to make the near future, the next verb stays in the infinitive.

Pattern:

• je vais manger
• tu vas partir
• il va dormir

This is similar to English to be going to + verb:

• He is going to sleep

You do not conjugate both verbs. Only aller is conjugated here.

French separates these two expressions more clearly than English often does.

• bonsoir = good evening
• bonne nuit = good night

You say bonsoir when greeting someone in the evening, or sometimes when arriving somewhere at night.

You say bonne nuit when someone is going to bed, going to sleep, or when you are parting for the night.

Since Paul va dormir, bonne nuit fits the situation.

Because nuit is a feminine noun in French.

So the adjective bon has to agree with it:

• masculine: bon
• feminine: bonne

Examples:

• bon jour does not exist as a normal phrase; the fixed expression is bonjour
• bonsoir is masculine in form
• bonne nuit is feminine because nuit is feminine

Because bonne nuit is a fixed expression, like a greeting or wish.

French often leaves out articles in set phrases of this kind:

• bonjour
• bonsoir
• bonne nuit
• merci

You are not talking about a good night in a general sense; you are using the expression good night.

Not necessarily, if the listener already understands who you are speaking to.

• Je dis bonne nuit. = I say good night.
• Je dis bonne nuit à Paul. = I say good night to Paul.
• Je lui dis bonne nuit. = I say good night to him.

In real conversation, French often includes lui if the person matters in the sentence:

• Paul va dormir ; je lui dis bonne nuit.

So the original sentence is understandable, but adding lui can sound more explicit and natural.

Yes, it is understandable and grammatically fine. But in everyday French, speakers often prefer slightly fuller or more idiomatic versions, such as:

• Je lui dis bonne nuit.
• Je dis bonne nuit à Paul.

Also, depending on context, a French speaker might say:

• Paul va se coucher ; je lui dis bonne nuit.

That is because aller se coucher often sounds more natural than aller dormir when talking about going to bed.

So the sentence works, but there are versions that may sound more natural in ordinary speech.

Yes, both are possible, but they mean slightly different things.

• je dis bonne nuit = I say good night / I am saying good night
• je vais dire bonne nuit = I am going to say good night

The present tense can describe an action happening now or as part of the situation being described. If you want to emphasize that your saying good night is still about to happen, je vais dire bonne nuit would be more future-oriented.

So the original sentence presents the second action more directly, while je vais dire would make it more clearly parallel with Paul va dormir.

The semicolon links two closely related clauses:

• Paul va dormir
• je dis bonne nuit

It shows a stronger break than a comma, but a weaker break than a full stop.

In English, you could also write:

• Paul is going to sleep; I say good night.

In French, the semicolon is used in much the same way to connect related ideas.

That is standard French typography.

In French, many punctuation marks take a space before them, especially:

• ;
• :
• ?
• !

So:

• Paul va dormir ; je dis bonne nuit.

looks normal in French typography, even though English normally does not put a space before a semicolon.

Often, yes.

• aller dormir = to go sleep / to go and sleep
• aller se coucher = to go to bed

If you are talking about the bedtime moment, French often prefers se coucher. That is because dormir focuses on the sleeping itself, while se coucher focuses on the act of going to bed.

So:

• Paul va dormir is correct
• Paul va se coucher may sound more idiomatic in many everyday contexts

Yes, this is one case where the French structure matches English quite closely.

• dire = to say
• bonne nuit = good night

So dire bonne nuit à quelqu’un means to say good night to someone.

Just remember that French often adds the indirect object more clearly:

• Je lui dis bonne nuit
• Je dis bonne nuit à Paul