Wp-cli Couldn’t install language

I have a wordpress project installed via composer with bedrock configuration.

I use capistrano for deployment.

Here, my composer.json file:

{
  "name": "my-project",
  "type": "project",
  "autoload": {
    "psr-0": {"Roots\Bedrock\Installer": "scripts"}
  },
  "repositories": [
    {
      "type": "composer",
      "url": "http://wpackagist.org"
    }
  ],
  "require": {
    "php": ">=5.5",
    "composer/installers": "~1.0",
    "vlucas/phpdotenv": "~1.0",
    "johnpbloch/wordpress": "~4.1",
    "wp-cli/wp-cli": "~0.18"
  },
  "scripts": {
    "post-root-package-install": ["Roots\Bedrock\Installer::addSalts"]
  },
  "config": {
    "bin-dir": "bin",
    "generate-salts": true
  },
  "minimum-stability": "dev",
  "prefer-stable": true,
  "extra": {
    "installer-paths": {
      "web/app/mu-plugins/{$name}/": ["type:wordpress-muplugin"],
      "web/app/plugins/{$name}/": ["type:wordpress-plugin"],
      "web/app/themes/{$name}/": ["type:wordpress-theme"]
    },
    "wordpress-install-dir": "web/wp"
  }
}

I want to install the fr_FR language, so I ran the following wp-cli command:

./bin/wp core language install fr_FR

This works like a charm on local, but not on the server after a capistrano deployment. I want to debug it but I got nothing else than this error:

htdocs/current$ ./bin/wp --debug core language install fr_FR
Error: Couldn't install language.

Is someone had this issue? How to solve it?

Many thanks.