How to refresh next-i18next content update automatically?

tl;dr

If you want to refresh your Next.js app using next-i18next automatically, you can do it like below:

import { GetStaticProps } from "next";
import { i18n } from "next-i18next";
import { serverSideTranslations } from "next-i18next/serverSideTranslations";
import { useRouter } from "next/router";
import { useEffect } from "react";
import Home from "../components/home";

export const getStaticProps: GetStaticProps = async ({ locale }) => {
  if (process.env.NODE_ENV === "development") {
    await i18n?.reloadResources();
  }
  return {
    props: {
      ...(await serverSideTranslations(locale!, ["common"])),
    },
  };
};

const Index = () => {
  if (process.env.NODE_ENV === "development") {
    const router = useRouter();
    useEffect(() => {
      const timer = setInterval(() => {
        router.replace(router.asPath, undefined, {
          scroll: false,
        });
      }, 5000);
      return () => clearTimeout(timer);
    });
  }
  return <Home />;
};

export default Index;

What was the issue?

When I started using next-i18next, I realized next dev server only loaded the translation files once when initialized and never updated even if I reloaded the page on my browser since server side doesn't change. Whenever I updated the translation, I needed to restart next dev server, which was bad developer experience.

Alternative solutions

That is a known limitation and there are multiple GitHub issues like this. I was able to find two approaches:

Restart next dev automatically whenever the content is updated.
Poll API endpoint to monitor the content update and refresh the content.

The option 1 is simple and nodemon can easily achieve the goal. However, this is not "Fast Refresh" and takes a while.

The option 2 seems better because next dev server keeps running, but too complicated to implement internal API. It can be done without API like next-remote-watch which monitors files and calls Next.js's internal method to reload the page. I tried it but it still requires implementation of content refresh by calling i18n.reloadResources() anyway. Also, page refresh is not "Fast Refresh" neither.

Solution

Then, I realized this can be done much simpler. First of all, it anyway requires polling from client side because there is no public method to execute "Fast Refresh" from Next.js server side. Using internal method like next-remote-watch does is not sustainable. Therefore, client side polling is the best way.

However, setting up an API (i.e. /api/something) for such a simple polling seems overkill. I thought it's probably enough by just re-rendering the page. With this approach, unless the virtual DOM of React has been updated, nothing happens on client side (I think).

Now, how I can tell the translation files' change to the client? Next.js has a good mechanism to provide props to page i.e. GetStaticProps which is already used by next-i18next installation. I found a great solution to trigger this from client side.

In addition, I found that it can call i18n.reloadResources() there because i18n instance is stored in a global value. I lazily implemented it with reloading i18n at every request because my project doesn't have large translation files. This can eliminate file watcher logic at all.

Conclustion

Now, by adding a simple SetInterval() to refresh the page every 5 seconds on client side and reloading i18n on every GetStaticProps call, my Next.js pages are always in sync within 5 seconds. This is Next.js/React refresh, not browser refresh nor server restart, thus it's fast enough.

Let me know if you have a better solution or if you find a drawback of this solution :)

Notes

When your URL has hash (#foo), router.replace() always scrolls up to the anchor and doesn't reload preps from the server. This is a known issue and there is a discussion on GitHub repository: https://github.com/vercel/next.js/discussions/13804