In French, to say "the most" or "the least," you use a definite article (le, la, or les) followed by plus (most) or moins (least). But when you form a superlative with an adjective that naturally comes after the noun, there is a special rule: you must repeat the definite article.
Repeating the definite article
When an adjective follows the noun, the superlative requires the definite article to appear twice: once before the noun, and once again before plus.
[Definite Article] + [Noun] + [Definite Article] + plus + [Adjective]
Notice how the article la is used for the noun, and then repeated before the superlative in these examples about interior design:
| We like the contemporary decoration. | Nous aimons la décoration contemporaine. |
| It is the most contemporary decoration. | C'est la décoration la plus contemporaine. |
The second article must agree in gender and number with the noun. If the noun is masculine, you will use le twice:
| They chose the sleekest wooden floor. | Ils ont choisi le parquet le plus épuré. |
Nouns starting with a vowel
If your noun begins with a vowel or silent h, the first definite article will contract to l'. However, the second definite article comes right before the word plus (which starts with a consonant), so it will take its full, uncontracted form (le or la).
| It is the most harmonious layout. | C'est l'agencement le plus harmonieux. |
Plural superlatives
The rule remains exactly the same for plural nouns. You simply use les before the noun, and les again before plus.
| We are buying the lightest wallpapers. | Nous achetons les papiers peints les plus clairs. |