Nous essayons de colmater la fuite avant que la pluie ne recommence.

The verb essayer is very commonly followed by de + infinitive:

• essayer de faire quelque chose = to try to do something

So:

• Nous essayons de colmater la fuite = We are trying to seal/patch the leak

You may also sometimes see essayer + infinitive without de, especially in modern usage:

• J’essaie comprendre is much less standard-sounding than J’essaie de comprendre
• J’essaie de comprendre is the safest choice

So for learners, essayer de + infinitive is the best pattern to remember.

Colmater means to stop up, plug, seal, or patch, especially when something is leaking.

It is more specific than a general verb like réparer (to repair).
For example:

• réparer la fuite = repair the leak
• colmater la fuite = patch/plug the leak so it stops leaking

So colmater gives the idea of blocking the opening or sealing the source of the leak.

Yes. Fuite can mean different things depending on context:

• a leak
• an escape
• a flight/running away

In this sentence, because of colmater and pluie, la fuite clearly means the leak.

This is very common in French: one noun can have several related meanings, and the context tells you which one is intended.

Because the infinitive is essayer, and in the nous form the spelling stays essayons.

Conjugation:

• j’essaie / j’essaye
• tu essaies / essayes
• il essaie / essaye
• nous essayons
• vous essayez
• ils essaient / essayent

For many -ayer verbs, French allows variation in some forms, but nous and vous normally keep y:

• nous essayons
• vous essayez

So essayons is the expected spelling.

Use avant de + infinitive when the subject stays the same.
Use avant que + clause when a new subject is introduced.

Here, the first subject is nous, but the second subject is la pluie:

• Nous essayons de colmater la fuite
• avant que la pluie ne recommence

Because the subject changes, French needs a full clause after avant que.

Compare:

• Je pars avant de manger = same subject (I leave before eating)
• Je pars avant qu’il n’arrive = different subject (I leave before he arrives)

Because avant que normally requires the subjunctive.

So after avant que, you get:

• avant que la pluie ne recommence

Here recommence is the present subjunctive of recommencer.

This happens because avant que introduces something that has not happened yet at the moment being described. French often uses the subjunctive after expressions involving uncertainty, anticipation, emotion, judgment, or something not yet realized.

A few examples:

• Attends jusqu’à ce qu’il vienne.
• Pars avant qu’elle n’arrive.

So in this sentence, the subjunctive is required by the expression avant que.

No, it is not negative.

This ne is called the expletive ne (sometimes ne explétif). It appears after certain expressions, including avant que, but it does not mean not.

So:

• avant que la pluie ne recommence

still means:

• before the rain starts again
• not before the rain does not start again

This extra ne is mostly a grammatical/stylistic feature. It is common in careful written or formal French after expressions like:

• avant que
• de peur que
• à moins que

In everyday speech, people may omit it, but you should definitely recognize it when reading.

French uses articles much more often than English does.

In English, we can say:

• before rain starts again
• before the rain starts again

French normally needs an article here, so it says:

• avant que la pluie ne recommence

With weather nouns like la pluie, le vent, la neige, French usually uses the definite article when speaking about the phenomenon in general or the specific weather situation being discussed.

So la pluie sounds natural, while bare pluie would not work here.

Both ideas are understandable, but recommencer is the natural single verb for to start again.

• recommencer = to begin again / to start again

So:

• la pluie recommence = the rain starts again

You could also express a similar idea in other ways depending on style, but recommencer is direct and idiomatic here.

Yes.

The French present tense often covers both the English simple present and present progressive:

• Nous essayons = We try / We are trying

In this sentence, the context strongly suggests We are trying, because it describes an action in progress:

• Nous essayons de colmater la fuite avant que la pluie ne recommence.

So even though French does not use a separate am/is/are + -ing form here, the meaning is naturally progressive.