How does Next >= 13 detect locale? Can't get locale to switch depending on domain, using next-translate

[PhilipAngelinNE]

Summary

My team built a bunch of Next 12 apps with next-translate, all went smoothly. We don't use language slugs in the path or anything. Rather we let Next handle it, which I can only assume it did by the domain. We have a .se and .de domain respectively for this frontend, one for each tenant.

As far as I know we didn't do anything manually. We have no i18n in those Next apps' configs or anything. We pretty much just let Next handle it out of the box.

But ever since making the first Next >= 13 app recently, I noticed that the locale is hard stuck on "sv" regardless of which domain I visit. I even tried adding the i18n portion, including the domains array, in Next the config but no.

The defaultLocale that I provide to next-translate is the one it'll be stuck on. I tried manually setting my client Accept-Language header to "en", "sv", and "de" respectively, but Next kept sticking to the defaultLocale set in the next-translate config. I have tried switching the localeDetection to true and back as well, it doesn't budge.

Here is the Next config:

const withNx = require('@nrwl/next/plugins/with-nx');
const withNextTranslate = require('next-translate-plugin');

const assetPrefix = '/ency-junior-assets';

/**
 * @type {import('@nrwl/next/plugins/with-nx').WithNxOptions}
 **/
const nextConfig = {
  typescript: {
    ignoreBuildErrors: true,
  },
  transpilePackages: [],
  experimental: {
    appDir: true,
  },
  assetPrefix,
  webpack(config, options) {
    config.module.rules.push({
      test: /\.gql/,
      use: [options.defaultLoaders.babel, { loader: '@bustle/graphql-loader' }],
    });
    return config;
  },
  nx: {
    svgr: true,
  },
  images: {
    dangerouslyAllowSVG: true,
    domains: [ ... ],
    path: `${assetPrefix}/_next/image`,
  },
  serverRuntimeConfig: {
    cloudinaryHost: process.env.NEXT_PUBLIC_CLOUDINARY_HOST,
    tenants: process.env.NEXT_TENANTS,
  },
  publicRuntimeConfig: {
    cloudinaryHost: process.env.NEXT_PUBLIC_CLOUDINARY_HOST,
    tenants: process.env.NEXT_TENANTS,
  },
};

module.exports = withNx(withNextTranslate(nextConfig));

And here is the i18n config for next-translate:

module.exports = {
  locales: ['en', 'sv', 'de'],
  defaultLocale: 'sv',
  localeDetection: false,
  pages: {
    '*': ['common'],
  },
};

We do use Nx as a monorepo to serve our apps. Nx version is 15.8.6.

next-translate version: 2.0.2
Next version: 13.1.1

Example

No response

[PhilipAngelinNE]

To put is very shortly; how come when I am on a .de domain with Accept-Language: "de" that Next still loads the fallback sv instead? Seemingly only happens in v13.