Dynamic Loading of Message Catalogs

I18nProvider doesn't assume anything about your app and it's the developer responsibility to load messages based on active language.

Here's an example of a basic setup with a dynamic load of catalogs.

Final i18n Loader Helper

Here's the full source of i18n.ts logic:

i18n.ts

import { i18n } from "@lingui/core";

export const locales = {
  en: "English",
  cs: "Česky",
};
export const defaultLocale = "en";

/**
 * We do a dynamic import of just the catalog that we need
 * @param locale any locale string
 */
export async function dynamicActivate(locale: string) {
  const { messages } = await import(`./locales/${locale}/messages`);
  i18n.load(locale, messages);
  i18n.activate(locale);
}

How should I use the dynamicActivate in our application?

import React, { useEffect } from "react";
import App from "./App";

import { I18nProvider } from "@lingui/react";
import { i18n } from "@lingui/core";
import { defaultLocale, dynamicActivate } from "./i18n";

const I18nApp = () => {
  useEffect(() => {
    // With this method we dynamically load the catalogs
    dynamicActivate(defaultLocale);
  }, []);

  return (
    <I18nProvider i18n={i18n}>
      <App />
    </I18nProvider>
  );
};

Conclusion

Looking at the content of build dir, we see one chunk per language:

i18n-0.c433b3bd.chunk.js
i18n-1.f0cf2e3d.chunk.js
main.ab4626ef.js

When page is loaded initially, only main bundle and bundle for the first language are loaded:

After changing language in UI, the second language bundle is loaded: