Locale payload seems to contain all languages

[neverether]

I'm using next-i18next with NextJS 12 in production, and we've got quite a lot of localization in our codebase. On most routes we're running into data-too-large warnings from Next simply due to the localization sheets. Digging a bit deeper, I'm finding that both en and ja locales (the two locales we support) are both included in the [page].json response during hydration:

(images cropped to avoid sensitive data)

The Readme clearly states only the language in use should be sent to the client but it doesn't seem to be the case: https://github.com/i18next/next-i18next#5-declaring-locale-dependencies

Before I open an issue I'd like to verify that's indeed what's happening here. Is this happening to anyone else?

EDIT:
My config is as follows:

/** @type import("next").I18NConfig */
const i18n = {
  defaultLocale: "ja",
  locales: ["en", "ja"],
  localeDetection: true,
};

/** @type import("next-i18next").UserConfig */
const next18nextConfig = {
  i18n,
  defaultNS: "home",
  localePath: path.resolve("./public/locales"),
  reloadOnPrerender: isDev, // reloads the page when JSON files change – this needs to be off in production
};

[adrai]

Seems to work, also the test proofs this: https://github.com/i18next/next-i18next/blob/master/src/serverSideTranslations.test.tsx#L294
I assume your detected language is en and since your defaultLocale is ja and is always loaded as fallback, en and ja area loaded.

[neverether]

Ah you're correct, when I load a ja route, I'm only getting the Japanese locale data. Out of curiosity, what purpose does always loading the defaultLocale as a fallback achieve? In my experience, the fallback always ends up being the translation's key anyway.

[adrai]

Normally, the defaultLocale is your reference language... so showing that is better than showing only keys.

[neverether]

I can see how that would be preferable to keys – I personally find that a lot of users will ignore English they can't read instead of speaking up – we get more reports of missing keys when they're obviously wrong. But each to their own!

Since our team doesn't care about that fallback, I was able to set fallbackLng: false in my config and now I'm only getting the active locale language from the server which was my intent from the beginning to slim down the payload as much as possible.