Mówimy dobranoc po quizie pubowym.

Mówimy is the 1st person plural present tense of mówić, so it means we say or, depending on context, we are saying.

In a sentence like this, it most naturally sounds general or habitual:

• Mówimy dobranoc po quizie pubowym. = this is what we say / this is what happens after the pub quiz.

If you wanted to talk about one completed past event, you would normally use a different form:

• Powiedzieliśmy dobranoc po quizie pubowym. = we said goodnight after the pub quiz

So mówimy fits a general statement well.

Because Polish usually drops subject pronouns when they are already clear from the verb ending.

The ending -my in mówimy already tells you the subject is we.

So:

• Mówimy = we say
• My mówimy = we say, but with extra emphasis, contrast, or clarification

For example:

• My mówimy dobranoc, a oni jeszcze zostają.
  = We say goodnight, but they are still staying.

Because dobranoc is a fixed Polish expression meaning goodnight.

Compare:

• dobranoc = the set farewell expression
• dobra noc = literally a good night

So:

• Mówimy dobranoc. = We say goodnight.
• To była dobra noc. = It was a good night.

This is a very common thing in Polish: some expressions become fixed as a single word.

It is mainly a farewell, not a greeting.

You say dobranoc:

• when leaving late in the evening or at night
• when going to sleep
• when ending contact for the night

You normally do not use it to say hello at night. For that, Polish usually uses:

• dobry wieczór = good evening

So:

• arriving at a place in the evening: dobry wieczór
• leaving for the night: dobranoc

Because with mówić, Polish often uses greeting and farewell expressions in their fixed form, without changing them.

So you say:

• mówić dobranoc
• mówić dzień dobry
• mówić cześć

But if you use a different verb, the structure may change:

• życzymy dobrej nocy = we wish you a good night

So:

• mówić dobranoc = to say goodnight
• życzyć dobrej nocy = to wish someone a good night

Those are different constructions.

Because the preposition po meaning after requires the locative case.

The dictionary form is:

• quiz

But after po, it changes to:

• po quizie

This is very common in Polish:

• po pracy = after work
• po obiedzie = after lunch
• po meczu = after the match
• po quizie = after the quiz

So the change is caused by the preposition po.

Because pubowym is an adjective, and it has to match the noun quizie in:

• case
• number
• gender

Here the noun is:

• quizie = locative singular

So the adjective must also be locative singular masculine:

• pubowy → pubowym

You can think of it like this:

• dictionary form: quiz pubowy
• after po: po quizie pubowym

Both words change as needed inside the noun phrase.

In Polish, adjectives often come before the noun, but they can also come after it.

So both of these are possible:

• po quizie pubowym
• po pubowym quizie

The version with the adjective after the noun can sound a bit more like a set label or type of event, while the version with the adjective before the noun may feel more neutral to many learners.

The important point is that Polish word order inside noun phrases is more flexible than in English, though not completely free.

Yes. It is a loanword from English, but it behaves like a normal Polish noun and takes Polish endings.

For example:

• quiz
• quizu
• quizie
• quizem

That is very common in Polish: borrowed words are often fully integrated into Polish grammar.

So even though quiz looks English, in Polish it declines like other nouns.

Yes. Polish word order is quite flexible, and changing it often changes emphasis rather than basic meaning.

For example:

• Mówimy dobranoc po quizie pubowym.
  Neutral statement.

• Po quizie pubowym mówimy dobranoc.
  Puts more focus on after the pub quiz.

• Dobranoc mówimy po quizie pubowym.
  More marked, with extra emphasis on dobranoc.

So the original word order is natural, but it is not the only possible one.

This is about aspect, which is very important in Polish verbs.

• mówić = imperfective
• powiedzieć = perfective

Very roughly:

• mówić focuses on the action as a process, habit, or general fact
• powiedzieć focuses on a completed act of saying something

So:

• Mówimy dobranoc po quizie pubowym.
  = We say goodnight after the pub quiz.
  This sounds general/habitual.

• Powiemy dobranoc po quizie pubowym.
  = We will say goodnight after the pub quiz.
  Future, one completed act.

• Powiedzieliśmy dobranoc po quizie pubowym.
  = We said goodnight after the pub quiz.
  Past, completed act.

So mówimy is the right choice if the sentence is describing a usual pattern.