i18n.js

const i18next = require('i18next');
const XHR = require('i18next-xhr-backend');
const LanguageDetector = require('i18next-browser-languagedetector');

const options = {
  fallbackLng: 'en',
  load: 'languageOnly', // we only provide en, de -> no region specific locals like en-US, de-DE

  // have a common namespace used around the full app
  ns: ['common'],
  defaultNS: 'common',

  debug: process.env.NODE_ENV !== 'production',
  saveMissing: true,

  interpolation: {
    escapeValue: false, // not needed for react!!
    formatSeparator: ',',
    format: (value, format, lng) => {
      if (format === 'uppercase') return value.toUpperCase();
      return value;
    },
  },
};

const i18nInstance = i18next;

// for browser use xhr backend to load translations and browser lng detector
if (process.browser) {
  i18nInstance
    .use(XHR)
    // .use(Cache)
    .use(LanguageDetector);
}

// initialize if not already initialized
if (!i18nInstance.isInitialized) i18nInstance.init(options);

// a simple helper to getInitialProps passed on loaded i18n data
const getInitialProps = (req, namespaces) => {
  if (!namespaces) namespaces = i18nInstance.options.defaultNS;
  if (typeof namespaces === 'string') namespaces = [namespaces];

  req.i18n.toJSON = () => null; // do not serialize i18next instance and send to client

  const initialI18nStore = {};
  req.i18n.languages.forEach(l => {
    initialI18nStore[l] = {};
    namespaces.forEach(ns => {
      initialI18nStore[l][ns] =
        (req.i18n.services.resourceStore.data[l] || {})[ns] || {};
    });
  });

  return {
    i18n: req.i18n, // use the instance on req - fixed language on request (avoid issues in race conditions with lngs of different users)
    initialI18nStore,
    initialLanguage: req.i18n.language,
  };
};

module.exports = {
  getInitialProps,
  i18nInstance,
  I18n: i18next.default,
};