La grille de vétusté réduit la retenue.

French often uses the definite article where English would sometimes leave it out.

So la grille de vétusté means the wear-and-tear scale/table. In French, it sounds normal to include la here because you are talking about a specific type of thing, not just the concept in general.

The same is true for la retenue: French naturally says the deduction/withholding, where English might sometimes just say a deduction or even omit an article depending on context.

De vétusté means something like for wear and tear, related to wear and tear, or based on age/usage deterioration.

The structure noun + de + noun is extremely common in French. It links two nouns together, often like English of or sometimes like an adjective:

• une table de cuisine = a kitchen table
• un contrat de location = a rental contract
• une grille de vétusté = a wear-and-tear scale/table

Here, de connects grille and vétusté.

Because this is a fixed descriptive structure: grille de vétusté.

When French uses noun + de + noun to classify or describe something, it often does not use an article after de:

• une tasse de café
• une salle de bain
• une grille de vétusté

If you said de la vétusté, that would sound more like some wear and tear or of the wear and tear, which is not the usual label for this kind of document or scale.

Réduit is the 3rd person singular present form of the verb réduire (to reduce).

The subject is La grille de vétusté, which is singular, so the verb must also be singular:

• je réduis
• tu réduis
• il/elle/on réduit
• nous réduisons
• vous réduisez
• ils/elles réduisent

So:

• La grille ... réduit ... = The scale/table reduces ...

In French, a verb agrees with the subject in person and number, but usually not in gender.

So whether the subject is masculine or feminine, the present-tense verb form is the same:

• Le document réduit la retenue.
• La grille réduit la retenue.

Both use réduit because both subjects are 3rd person singular.

Gender matters for articles and adjectives, but not for this verb form in the present tense.

Yes — retenue has more than one meaning in French.

It can mean:

• restraint / self-control
• withholding
• deduction or amount kept back

In this sentence, it does not mean self-control. It means something like the deduction, the withheld amount, or the amount charged/kept back.

That is very common in French: the same noun can have different meanings depending on context.

Yes. This sentence follows the basic French word order:

• La grille de vétusté = subject
• réduit = verb
• la retenue = direct object

So it is a very standard subject–verb–object sentence, just like English:

• The wear-and-tear scale reduces the deduction.

French often works this way in simple declarative sentences.

Yes. That is the passive version:

• La grille de vétusté réduit la retenue. = active
• La retenue est réduite par la grille de vétusté. = passive

Both are grammatical, but the active sentence is usually more direct and natural unless you specifically want to emphasize la retenue.

Approximate pronunciation:

• réduit ≈ ray-dwee
• vétusté ≈ vay-too-stay
• retenue ≈ ruh-tuh-new

A few notes:

• é sounds like a clear ay sound.
• u in French is not exactly like English oo. It is a front rounded vowel, which English speakers often need practice with.
• The final t in réduit is usually silent.

The accents help show pronunciation and distinguish correct spelling.

• é gives a clear ay sound.
• In vétusté, both accented é sounds are pronounced.
• In réduit, the é also has that ay sound.

So the accents are not optional decorations — they are part of the correct spelling and help indicate how the word is said.

Sometimes, but not always.

Grille can mean things like:

• a grid
• a grille/grate
• a table/chart/scale depending on context

In grille de vétusté, it does not mean a cooking grill. It means something more like a scale, chart, or reference table used to calculate wear-and-tear deductions.

So this is a good example of a word whose meaning depends strongly on context.