getMessages.js

const jsonfile = require("jsonfile");
const preq = require("preq");

const DEFAULT_LANGS = ["en"];

const API_BASE_URL = `https://www.mediawiki.org/w/api.php`;

const MESSAGE_KEYS = [
  "login",
  "readinglists-browser-add-entry-success",
  "readinglists-browser-enable-sync-prompt",
  "readinglists-browser-error-intro",
  "readinglists-browser-extension-info-link-text",
  "readinglists-browser-list-entry-limit-exceeded",
  "readinglists-browser-login-prompt"
];

const ALLMESSAGES_QUERY = {
  action: "query",
  format: "json",
  formatversion: "2",
  meta: "allmessages",
  ammessages: MESSAGE_KEYS.join("|"),
  amenableparser: ""
};

function objToQueryString(obj) {
  return Object.keys(obj)
    .map(key => `${key}=${obj[key]}`)
    .join("&");
}

function allMessagesRequestUriForLang(lang) {
  return `${API_BASE_URL}?${objToQueryString(
    Object.assign(ALLMESSAGES_QUERY, { amlang: lang })
  )}`;
}

async function getMessages(langs) {
  const messages = {};

  await Promise.all(
    langs.map(async lang => {
      await preq.get({ uri: allMessagesRequestUriForLang(lang) }).then(res => {
        if (!(res.body && res.body.query && res.body.query.allmessages)) return;
        messages[lang] = {};
        res.body.query.allmessages.forEach(
          messageObj => (messages[lang][messageObj.name] = messageObj.content)
        );
      });
    })
  );

  return messages;
}

getMessages(DEFAULT_LANGS).then(messages => {
  Object.keys(messages).forEach(lang =>
    jsonfile.writeFile(
      `extension/i18n/${lang}.json`,
      messages[lang],
      { spaces: 2 },
      err => {}
    )
  );
  console.log("Wrote messages to i18n/[lang].json");
});