Intra domum silentium est, sed extra ianuam pueri rident.

Because intra and extra here are being used as prepositions that take the accusative.

• intra domum = inside the house
• extra ianuam = outside the door

So:

• domus → domum (accusative singular)
• ianua → ianuam (accusative singular)

This is something English speakers often have to get used to: in Latin, the preposition often determines the case of the noun that follows.

It can be either a preposition or an adverb.

In this sentence, intra is a preposition because it is followed by a noun, domum.

• intra domum = inside the house

But in other contexts, intra can also stand on its own more like an adverb, meaning inside or within.

The same is true of extra: it can also function as a preposition or an adverb depending on the sentence.

Both can relate to being in/inside a place, but they are not exactly the same in feel.

• in domo usually means in the house
• intra domum means more specifically inside the house, often emphasizing within as opposed to outside

So intra domum contrasts very neatly with extra ianuam:

• inside the house
• outside the door

That contrast is probably why this wording was chosen.

Latin has no articles like English the or a/an.

So a noun like domum can mean:

• a house
• the house

and pueri can mean:

• boys
• the boys

You figure out which is meant from the context. In this sentence, English naturally translates them with the.

Because silentium is singular.

• silentium = silence
• est = is

So silentium est literally means there is silence or silence is present.

Latin often uses est in this way, where English might say it is quiet or there is silence.

If the subject were plural, then Latin would use sunt.

Here pueri is nominative plural, so it means the boys and is the subject of rident.

We know this because:

• rident is a 3rd person plural verb: they laugh
• therefore the subject must be plural
• pueri fits perfectly as boys

A learner may notice that pueri can also be genitive singular in some contexts (of the boy), but that does not fit here, because the sentence needs a subject for rident.

Rident is the 3rd person plural present active indicative of rideo, ridere, meaning to laugh.

So:

• rideo = I laugh
• rides = you laugh
• ridet = he/she/it laughs
• rident = they laugh

Since pueri is plural, the verb must also be plural: pueri rident = the boys laugh.

Latin word order is much more flexible than English word order because Latin shows grammatical relationships mostly through endings, not just position.

English depends heavily on word order:

• The boys laugh is not the same as Laugh the boys

Latin can move words around more freely without changing the basic meaning:

• Intra domum silentium est
• Silentium intra domum est

Both can mean roughly the same thing.

In this sentence, the order is natural and expressive:

• Intra domum comes first to set the scene
• sed marks the contrast
• extra ianuam pueri rident gives the contrasting image

So the word order helps the style and emphasis.

Yes, literally it is silence is or more naturally there is silence.

Latin often expresses ideas in a way that English would phrase differently. A more idiomatic English rendering might be:

• It is quiet inside the house
• There is silence inside the house

So the Latin is perfectly normal; it just does not map word-for-word into the most natural English structure.

Sed means but, and it sets up a clear contrast between the two halves of the sentence:

• inside the house → silence
• outside the door → the boys are laughing

So sed is important because it highlights the opposition between quiet and noise, and between inside and outside.

They refer to different things:

• domus = house, home
• ianua = door or main entrance

So:

• intra domum = inside the house
• extra ianuam = outside the door

The sentence moves from the larger space (the house) to a boundary point (the door), which makes the contrast vivid.

Yes, that would also be possible Latin, but it would mean something slightly different.

• extra domum = outside the house
• extra ianuam = outside the door

The version with ianuam focuses more closely on the doorway or entrance area. It creates a sharper contrast with intra domum: silence is inside, but right outside the door the boys are laughing.

A classical-style pronunciation would be approximately:

In-tra do-mum si-len-ti-um est, sed ex-tra ya-nu-am pu-e-ri ri-dent.

A few useful points:

• c is always hard, though there is no c here
• i at the start of ianuam is pronounced like y
• ae does not appear here, but when it does, it is usually like ai in classical pronunciation
• r is trilled or tapped
• e in est is a clear vowel, not reduced like English unstressed vowels often are

So ianuam sounds roughly like ya-noo-am, not like English j-sound.

Yes, domum is a special form that learners often notice.

With words like domus and names of towns/small islands, Latin can sometimes use the accusative without a preposition to show motion toward:

• domum eo = I go home

But in your sentence, domum is not that special motion-toward use. Here it is simply the object of the preposition intra:

• intra domum = inside the house

So although domum does have a special use elsewhere, that is not what is happening here.