next-i18next/dist/es/middlewares/next-i18next-middleware.js

The easiest way to translate your NextJs apps.

import i18nextMiddleware from 'i18next-http-middleware/cjs';
import { addSubpath, lngFromReq, redirectWithoutCache, subpathFromLng, subpathIsPresent, subpathIsRequired } from '../utils';
export default function (nexti18next) {
  const {
    config,
    i18n
  } = nexti18next;
  const {
    allLanguages,
    ignoreRoutes
  } = config;

  const isI18nRoute = req => ignoreRoutes.every(x => !req.url.startsWith(x));

  const middleware = [];
  /*
    If not using server side language detection,
    we need to manually set the language for
    each request
  */

  if (!config.serverLanguageDetection) {
    middleware.push((req, _res, next) => {
      if (isI18nRoute(req)) {
        req.lng = config.defaultLanguage;
      }

      next();
    });
  }
  /*
    This does the bulk of the i18next work
  */


  middleware.push(i18nextMiddleware.handle(i18n));
  /*
    This does the locale subpath work
  */

  middleware.push((req, res, next) => {
    if (isI18nRoute(req) && req.i18n) {
      let currentLng = lngFromReq(req);
      const currentLngSubpath = subpathFromLng(config, currentLng);
      const currentLngRequiresSubpath = subpathIsRequired(config, currentLng);
      const currentLngSubpathIsPresent = subpathIsPresent(req.url, currentLngSubpath);
      const lngFromCurrentSubpath = allLanguages.find(l => subpathIsPresent(req.url, subpathFromLng(config, l)));

      if (lngFromCurrentSubpath !== undefined && lngFromCurrentSubpath !== currentLng) {
        /*
          If a user has hit a subpath which does not
          match their language, give preference to
          the path, and change user language.
        */
        req.i18n.changeLanguage(lngFromCurrentSubpath);
        currentLng = lngFromCurrentSubpath;
      } else if (currentLngRequiresSubpath && !currentLngSubpathIsPresent) {
        /*
          If a language subpath is required and
          not present, prepend correct subpath
        */
        return redirectWithoutCache(res, addSubpath(req.url, currentLngSubpath));
      }
    }

    next();
  });
  return middleware;
}