Ni parolis pri parlamento.

In Esperanto, -is marks the past tense for all verbs.

So:

• paroli = to speak
• parolas = speak / am speaking / is speaking
• parolis = spoke / talked / was talking
• parolos = will speak

The root here is parol-, meaning speak, and -is tells you the action happened in the past.

It can match any of those in English, depending on context.

Esperanto has one simple past tense, so parolis does not force the same distinction that English makes between:

• spoke
• talked
• was talking

The situation or surrounding sentence tells you which English translation sounds best.

Pri means about, concerning, or regarding.

With the verb paroli, Esperanto normally uses pri to introduce the topic:

• paroli pri io = to speak about something

So Ni parolis pri parlamento follows a very common pattern.

Because parlamento is part of a prepositional phrase, not the direct object of the verb.

The ending -n is mainly used for:

• the direct object
• certain expressions of movement or time

But after pri, you normally use the basic noun form:

• pri parlamento = about parliament

So the structure is We spoke about parliament, not We spoke parliament.

Because all Esperanto nouns end in -o.

That means:

• parlamento is a noun
• it means parliament

This is one of the most regular features of Esperanto. For example:

• -o = noun
• -a = adjective
• -e = adverb

So as soon as you see -o, you know the word is a noun.

Esperanto often leaves out la when something is being mentioned in a general or non-specific way.

So:

• pri parlamento = about parliament in a general sense
• pri la parlamento = about the parliament, meaning a specific parliament

Whether la is needed depends on how definite the noun is in context.

Yes.

That would usually mean We spoke about the parliament, with a particular parliament in mind, such as:

• the parliament of one country
• the parliament already mentioned earlier
• the parliament both speaker and listener already know about

Without la, the sentence sounds more general.

Yes, very much so.

Paroli pri is the standard and natural pattern for speak about or talk about.

Examples:

• Ŝi parolis pri sia familio. = She talked about her family.
• Ni parolas pri la vetero. = We are talking about the weather.

So in your sentence, the grammar is completely straightforward and idiomatic.

Not really.

Even though they look similar, Esperanto treats them as different roots:

• parol- = speak
• parlament- = parliament

So parlamento is not normally understood as a word built inside Esperanto from parol-. It is basically an international-style word that Esperanto uses as its own noun.

The given order is the most neutral one:

• Ni = subject
• parolis = verb
• pri parlamento = prepositional phrase

So Ni parolis pri parlamento is the ordinary, natural way to say it.

Esperanto word order is fairly flexible, though, so for emphasis you could also say:

• Pri parlamento ni parolis

But the original version is the standard one most learners should use first.

A rough English-friendly guide is:

nee pah-RO-lees pree pahr-lah-MEN-to

A few useful pronunciation points:

• Ni sounds like nee
• pri sounds like pree
• stress usually falls on the second-to-last syllable
  • pa-RO-lis
  • par-la-MEN-to
• the vowels stay regular and clear, unlike in English, where vowel sounds often shift a lot