Nous allons boucher ce trou avant qu’il pleuve encore.

In this sentence, aller + infinitive is the very common French way to express the near future:

• nous allons boucher = we are going to fill / plug / seal

Even though aller literally means to go, in this pattern it works like English be going to + verb.

So:

• nous allons = we are going to
• boucher = the main action

This is different from the simple present nous bouchons, which would usually mean we fill / we are filling depending on context.

The verb boucher takes a direct object, so it connects straight to the thing being blocked, plugged, or filled:

• boucher un trou = to fill / plug a hole
• boucher une bouteille = to cork/stopper a bottle
• boucher une issue = to block an exit

So ce trou is simply the direct object of boucher. No preposition is needed.

Ce trou means this hole or that hole, depending on context.

French demonstratives work a bit differently from English:

• ce
  • masculine singular noun
• cette
  • feminine singular noun
• ces
  • plural noun

Since trou is masculine singular, French uses ce:

• ce trou

French ce can translate as either this or that in English. The situation usually makes it clear.

Because avant que is normally followed by the subjunctive in French.

So French says:

• avant qu’il pleuve

not

• avant qu’il pleut

This is one of the most important grammar points in the sentence. After avant que (before), the action has not happened yet at the moment being discussed, and French uses the subjunctive for that.

So:

• il pleut = indicative, it is raining
• qu’il pleuve = subjunctive, that it rain / before it rains

Because que becomes qu’ before a word starting with a vowel or a mute h.

So:

• que il → qu’il

This is just standard French contraction/elision to make pronunciation smoother.

You see the same thing in many places:

• que elle → qu’elle
• je ai → j’ai
• ne est → n’est

Pleuve is the present subjunctive form of the verb pleuvoir (to rain) for il.

The relevant forms are:

• il pleut = present indicative
• qu’il pleuve = present subjunctive

Since weather verbs usually use il, you most often see:

• il pleut
• qu’il pleuve

So in this sentence, pleuve is not a tense like the simple past or future; it is a mood choice required by avant que.

Because pleuvoir is generally used as an impersonal verb. English does the same thing with it rains.

The il here does not refer to a person or thing. It is just the grammatical subject needed by the verb.

So:

• il pleut = it is raining / it rains

This il is sometimes called a dummy subject or impersonal il.

Here, encore means something like again or more.

So:

• avant qu’il pleuve encore

suggests:

• before it rains again
• before it rains some more

The exact nuance depends on context:

• If it already rained earlier, encore may mean again
• If it is part of a continuing rainy period, it may feel more like any more / some more

In this sentence it comes after the verb:

• qu’il pleuve encore

That placement is very natural in French for again / still / more type adverbs.

Compare:

• Il pleut encore. = It’s still raining / It’s raining again.
• Il va encore pleuvoir. = It’s going to rain again.

Adverb placement in French does not always match English exactly, so it is good to learn expressions like this as chunks.

Use avant de + infinitive when the subject of both actions is the same.

Example:

• Nous allons manger avant de partir.
• We are going to eat before leaving.

Here, the second action is it rains, and the subject is not nous but impersonal il. Because the subjects are different, French uses:

• avant que + subjunctive

So:

• avant qu’il pleuve = correct

not:

• avant de pleuvoir in this sentence

Yes. That is a very natural English translation.

French nous allons boucher literally matches we are going to fill, but in many contexts English would simply say:

• We’ll fill this hole before it rains again.

So depending on tone and context, English might use:

• We are going to fill this hole before it rains again
• We’ll fill this hole before it rains again

Both can fit the French sentence.

A couple of things may stand out:

• avant ends with a nasal vowel
• qu’il is pronounced smoothly as one unit
• pleuve has the eu sound, which many English speakers find tricky

Also, in connected speech, the whole group flows together quite tightly:

• avant qu’il pleuve

A learner does not need to pronounce every written consonant strongly. The important thing is to keep the rhythm smooth and not separate que and il too much.