react-i18next

Is your feature request related to a problem? Please describe.

The current JSON format is v3 as mentioned in the README, but since late september i18next has gone into v21, and now uses a new v4 format (for pluralization, among other things, see [their migration guide](https://www.i18next.com/misc/migration-guide#v-20-x-x-to-v-21

hey, first of all i'd like to mention that I'm not using graphql at all in my project.

I'm creating my pages with createPages (in gatsby-node.js), everything works just fine beside the page that needs extra prop from the slug,

here how i create it

createPages({
    path: '/item',
    matchPath: '/item/:itemId',
    component: path.resolve('./src/pages/ShowItem.js'),
    context: {}

While the setup works fine running locally, the deployed to vercel app returns empty translations by loadTranslations in getServerSideProps

GET | https://app.vercel.app/_next/data/HZ7wajlS0AuNQGjuW_9so/en/app/dashboard.json

{"pageProps":{"__ni18n_server__":{"resources":{"en":{"dashboard":{},"common":{}}},"ns":["dashboard","common"]}},"__N_SSP":true}

ni18n.config.ts