I currently have this configuration in index.jsx:

i18n.use(LanguageDetector).init({
    detection: {
        caches: ['cookie'],
        cookieOptions: { sameSite: 'none' },
    },
});
i18n.use(initReactI18next) // passes i18n down to react-i18next
    .init({
        resources: {
            en: translation_en,
            fr: translation_fr,
        },
        fallbackLng: 'en',

        interpolation: {
            escapeValue: false,
        },
    });

And it does not store anything in cookies. If I replace the caches by localStorage, it works (in localStorage, not cookies, obviously).

This is the current configuration, but fyi, my initial one was this :

const BACKEND_DOMAIN = process.env.REACT_APP_BACKEND_DOMAIN;

i18n.use(LanguageDetector).init({
    detection: {
        cookieDomain: BACKEND_DOMAIN,
        caches: ['localStorage', 'cookie'],
        cookieOptions: { sameSite: 'none' },
    },
});

As I want the cookie to be sent to the backend api, so I can use the locale there.

I have no lead whatsoever, anyone got an idea?