I read in this blog post this sentence

Symfony Inflector component converts words between their singular and plural forms (for now, only in English)

So I created a FrenchInflector class implementing the InflectorInterface from the String component. This inflector uses regular expressions and it is tested in the FrenchInflectorTest with a lot of the french exceptions.

Changelog has been updated, but I'm not sure I did it in the good paragraph.

I don't know if I should update the symfony/symfony-docs, but I have created an example and I could create a PR with it, if you want.

<?php

use Symfony\Component\String\Inflector\FrenchInflector;

$inflector = new FrenchInflector();

$result = $inflector->singularize('dents');     // ['dent']
$result = $inflector->singularize('souris');    // ['souris']
$result = $inflector->singularize('messieurs'); // ['monsieur']

$result = $inflector->pluralize('cinquante'); // ['cinquante']
$result = $inflector->pluralize('pou');       // ['poux']
$result = $inflector->pluralize('cheval');    // ['chevaux']

fabbot.io is detecting a typo, but this is not. The patch done by fabpot suggests to replace the french 'embarras' word by 'embarrass'. I shall not remove or replace it, because "embarras" is an invariant word.