composer.json for latest Wordpress using johnpbloch/wordpress and languages.koodimonni.fi. This file has also an example of how to handle wordpress dropin-files (e.g. object-cache.php, sunrise.php, ...) using composer.json

composer.json

{
  "repositories": [
      {
          "type": "composer",
          "url": "https://wp-languages.github.io"
      },
      {
        "type": "composer",
        "url": "https://wpackagist.org"
      }
  ],
  "require": {
    "johnpbloch/wordpress": "*",

    "koodimonni-language/fi": "*",
    "koodimonni-language/ru_RU": "*",
    "koodimonni-language/fr_fr": "*",
    "koodimonni-language/en_gb": "*",
    "koodimonni-language/en_au": "*",
    "koodimonni-language/nl_nl": "*",
    "koodimonni-language/ca": "*",
    "koodimonni-language/az": "*",

    "wpackagist-plugin/wp-redis": "*",

    "wpackagist-theme/twentyfifteen": "*"
  },
  "extra": {
    "installer-paths": {
      "htdocs/wp-content/plugins/{$name}": ["type:wordpress-plugin"],
      "htdocs/wp-content/themes/{$name}": ["type:wordpress-theme"],
      "htdocs/wp-content/mu-plugins/{$name}": ["type:wordpress-muplugin"]
    },
    "dropin-paths": {
      "htdocs/wp-content/languages/": ["vendor:koodimonni-language"],
      "htdocs/wp-content/languages/plugins/": ["vendor:koodimonni-plugin-language"],
      "htdocs/wp-content/languages/themes/": ["vendor:koodimonni-theme-language"],
      "htdocs/wp-content/": ["package:wpackagist-plugin/wp-redis:object-cache.php"]
    },
    "wordpress-install-dir": "htdocs/wordpress"
  }
}