Sub porticu longa puellae inter columnas stant, dum pluvia in foro cadit.

Yes, puellae can have several meanings in isolation:

• nominative plural = girls
• genitive singular = of the girl
• dative singular = to/for the girl

In this sentence, it must be nominative plural because the verb is stant, which is they stand. So puellae stant means the girls stand.

Latin often relies on endings and verb forms together to show who is doing the action.

The ending -nt is the regular ending for 3rd person plural in the present tense in Latin.

So:

• stat = he/she/it stands
• stant = they stand

Because the subject is puellae = girls, the plural verb stant is required.

Because sub can take either:

• the ablative for location: under
• the accusative for movement toward/under

Here the girls are already standing in a place, not moving there, so Latin uses the ablative:

• sub porticu = under the portico

If the sentence described motion, you might see the accusative instead.

Because porticus is a fourth-declension noun.

Its ablative singular is porticu. That can look unusual if you are used to first- and second-declension endings like -a or -o.

A quick outline:

• nominative singular: porticus
• accusative singular: porticum
• ablative singular: porticu

So after sub with the ablative, porticu is exactly what we expect.

Longa agrees with porticu.

Latin adjectives must agree with the noun they describe in:

• gender
• number
• case

Here:

• porticu = feminine, singular, ablative
• longa = feminine, singular, ablative

So sub porticu longa means under the long portico.

In Latin, adjective placement is much freer than in English.

Both of these can be normal:

• longa porticu
• porticu longa

The meaning stays the same because the endings show the relationship. Word order in Latin often reflects emphasis or style more than strict grammar.

So porticu longa is not strange Latin at all.

Inter is a preposition that takes the accusative case.

So:

• inter = between, among
• columnas = accusative plural of columna

That gives:

• inter columnas = between the columns

Unlike sub or in, which can take different cases depending on meaning, inter normally just takes the accusative.

Because in with the ablative means in/on a place where something already is.

Here the rain is falling in the forum, so this is location, not motion:

• in foro = in the forum

By contrast, in with the accusative usually means motion into something.

So:

• in foro = in the forum
• in forum = into the forum

Dum here means while.

It connects the two actions:

• puellae ... stant = the girls are standing
• pluvia ... cadit = the rain falls / is falling

So dum shows that these actions are happening at the same time:

• while the rain is falling

Latin often uses the simple present where English may prefer either:

• falls
• is falling

So pluvia cadit can naturally mean:

• the rain falls
• the rain is falling

In context with dum, English usually sounds more natural with is falling, but the Latin present cadit is completely normal.

Latin often expresses weather more concretely than English.

Instead of using a dummy subject like it, Latin can simply use a noun and a verb:

• pluvia cadit = literally rain falls

That is a normal Latin way to describe rain.

So even though English prefers it is raining or rain is falling, the Latin structure is perfectly idiomatic.

A very literal unpacking is:

• Sub porticu longa = under the long portico
• puellae = the girls
• inter columnas = between the columns
• stant = stand
• dum = while
• pluvia = rain
• in foro = in the forum
• cadit = falls / is falling

So the sentence is something like:

• Under the long portico the girls stand between the columns, while rain falls in the forum.

Latin word order is flexible, but a common pattern is that the verb often comes near the end of its clause, as we see with stant and cadit.

Because Latin has no articles.

So a noun like puellae can mean:

• girls
• the girls

And porticu longa can mean:

• under a long portico
• under the long portico

The exact choice in English depends on the context and on what sounds natural in translation.