Nundinae in hoc pago omnibus gratae sunt, quia ibi et coloni et mercatores inter se conveniunt.

Yes, nundinae is a plural noun in Latin. It traditionally refers to the regular market days or market fair. Even when English might use something more singular-sounding like market day or the market, Latin often uses nundinae as a plural word.

That is why the sentence also has:

• gratae = plural
• sunt = plural

They all agree with nundinae.

Because gratae must agree with nundinae.

• nundinae is feminine plural
• so the adjective must also be feminine plural: gratae
• and the verb must be plural: sunt

So:

• grata est would be feminine singular
• grati sunt would be masculine plural
• gratae sunt is the correct match

Omnibus is dative plural, meaning to all or for all.

The adjective gratus, grata, gratum often works with the dative and means pleasing, welcome, or acceptable to someone.

So:

• omnibus gratae sunt = they are pleasing to everyone / everyone likes them

This is different from English, where we often say everyone likes the market days. Latin turns it around:

• the market days are pleasing to everyone

Pago is ablative singular because in takes the ablative when it means in or on in the sense of location.

So:

• in hoc pago = in this district / village / rural community

Compare:

• in hoc pago = in this district (location, so ablative)
• in hunc pagum = into this district (motion toward, so accusative)

Also, hoc is ablative singular masculine/neuter, agreeing with pago, which is masculine.

A pagus is a rural district, country area, village community, or local district. It is not quite the same as a big city.

So in hoc pago suggests a local country district or village setting, which fits well with coloni and mercatores meeting at market.

Et ... et ... means both ... and ....

So:

• et coloni et mercatores = both farmers/settlers and merchants

Latin could also simply say coloni et mercatores, but et ... et ... gives a slightly more balanced or emphatic sense:

• both the one group and the other group

Inter se means with one another, among themselves, or each other.

So:

• inter se conveniunt = they meet one another / they come together

Here it shows that the two groups are interacting with each other.

A useful way to understand it:

• inter = among, between
• se = themselves

Together: among themselves or with each other

Conveniunt is:

• 3rd person plural
• present tense
• active voice
• from convenire

It matches the compound subject:

• coloni et mercatores = the farmers and the merchants

So conveniunt means:

• they meet
• they come together
• they assemble

In this sentence, inter se conveniunt gives the sense they meet one another.

Ibi means there, and it refers back to the place already mentioned.

So the structure is roughly:

• The market days in this district are welcome to everyone, because there...

Latin often does this naturally: it names a place, then refers back to it with ibi.

This makes the second clause flow smoothly:

• quia ibi = because there

Yes, but it is also very normal Latin.

The sentence begins with Nundinae, putting the topic first:

• Nundinae in hoc pago omnibus gratae sunt...

Latin word order is more flexible than English because the endings show the grammar. Here the order helps emphasis and flow:

• Nundinae first: the topic
• in hoc pago: where
• omnibus: to whom they are pleasing
• gratae sunt: the main statement

Then the reason comes after:

• quia ibi et coloni et mercatores inter se conveniunt

An English speaker may want a more fixed order, but Latin often arranges words for emphasis rather than strict position.

Conveniunt by itself can already mean they come together or they meet. So yes, it could stand alone.

But inter se adds a clearer reciprocal idea:

• not just they gather
• but they meet one another

So inter se is not meaningless repetition; it sharpens the sense of mutual contact between coloni and mercatores.