react-i18next language is not set during tests with vitest

Question

Language is not set during tests with vitest. In a dependency I import, this code exists:

function useI18N() {
  var _useTranslation = reactI18next.useTranslation(),
      t = _useTranslation.t,
      language = _useTranslation.i18n.language;

  if (language !== 'nb' && language !== 'en') {
    throw Error('Language must be either nb or en.');
  }

  return t;
}

function withI18n(Component) {
  return function WrappedComponent(props) {
    var t = useI18N();
    return /*#__PURE__*/React__default["default"].createElement(Component, _extends({}, props, {
      i18n: t
    }));
  };
}

This code throws throw Error('Language must be either nb or en.'); when testing using vitest. It does not throw for building with vite nor with the previous test runner jest (with practically same config).

That code is wrapping a component that is consumed by several components up until the file I am testing, which is using this:

export const renderWithI18NContext = (
  component: ReactNode,
  organisation?: Organisation,
  locale = 'nb'
) => {
  return render(componentWithI18NContext(component, organisation, locale));
};

const componentWithI18NContext = (
  …
) => {
  store.dispatch(…);

  i18n.changeLanguage(locale);

  return (
    <Provider store={store}>
      {/* @ts-ignore */}
      <MemoryRouter>
        <SWRConfig value={{ dedupingInterval: 0 }}>
          <Some.Provider value={something}>
            {component}
          </Some.Provider>
        </SWRConfig>
      </MemoryRouter>
    </Provider>
  );
};

With an import i18n that looks like this:

use(initReactI18next).init({
  lng: 'nb',
  fallbackLng: 'nb',
  resources: {
    nb: {
      translation: {
        …
      }
    },
    en: {
      translation: {
        …
      }
    }
  },
  interpolation: {
    escapeValue: false // not needed for react as it escapes by default
  }
});

export default i18n;

Which is consumed like this:

it('should pass', async () => {
  renderWithI18NContext(
    <ComponentTestContainer>
      …
      component={<ComponentToTest {...props} />}
    />
  );

  expect(…);
});

I've narrowed it down to react-i18next is not picking up language, i.e., that use(initReactI18next).init({…}) is not called, or something..