datahub/examples/catalog/pages/_app.tsx

import { useEffect, useState } from 'react';
import { ApolloProvider } from '@apollo/react-hooks';
import { useApollo } from '../lib/apolloClient';
import { DEFAULT_THEME } from '../themes';
import { applyTheme } from '../themes/utils';
import I18nProvider from 'next-translate/I18nProvider';
import { useRouter } from 'next/router';
import '../styles/app.css';

interface I8nObject {
  [property: string]: any;
}

export async function loadNamespaces(
  namespaces: string[],
  lang: string
): Promise<I8nObject> {
  const res = {};
  for (const ns of namespaces) {
    res[ns] = await import(`../locales/${lang}/${ns}.json`).then(
      (m) => m.default
    );
  }
  return res;
}

type Props = {
  Component: any;
  pageProps: any;
};

const MyApp: React.FC<Props> = ({ Component, pageProps }) => {
  const apolloClient = useApollo(pageProps.initialApolloState);
  const [theme] = useState(DEFAULT_THEME); // setTheme
  const router = useRouter();

  useEffect(() => {
    /**
     * We can switch theme.
     * e.g. setTheme('primary');
     * */

    applyTheme(theme);
  }, [theme]);

  return (
    <I18nProvider lang={router.locale} namespaces={pageProps._ns}>
      <ApolloProvider client={apolloClient}>
        <Component {...pageProps} />
      </ApolloProvider>
    </I18nProvider>
  );
};

export default MyApp;