schon/storefront/composables/languages/useLanguageSwitch.ts

import {SWITCH_LANGUAGE} from "@/graphql/mutations/languages.js";
import {useAppConfig} from "~/composables/config";
import type {IUserResponse, LocaleDefinition} from "~/types";
import {DEFAULT_LOCALE} from "@intlify/core-base";

export function useLanguageSwitch() {
  const userStore = useUserStore();
  const router = useRouter();

  const { COOKIES_LOCALE_KEY } = useAppConfig();
  const switchLocalePath = useSwitchLocalePath();

  const cookieLocale = useCookie(
      COOKIES_LOCALE_KEY,
      {
        default: () => DEFAULT_LOCALE,
        path: '/'
      }
  );

  const isAuthenticated = computed(() => userStore.isAuthenticated)
  const userUuid = computed(() => userStore.user?.uuid);

  const { mutate, loading, error } = useMutation<IUserResponse>(SWITCH_LANGUAGE);

  async function switchLanguage(
      locale: string
  ) {
    cookieLocale.value = locale;
    await router.push({path: switchLocalePath(cookieLocale.value as LocaleDefinition['code'])})

    if (isAuthenticated.value) {
      const result = await mutate({
        uuid: userUuid.value,
        locale
      });

      if (result?.data?.updateUser) {
        userStore.setUser(result.data.updateUser.user)
      }
    }
  }

  watch(error, (err) => {
    if (err) {
      console.error('useBrands error:', err)
    }
  });

  return {
    switchLanguage,
    loading
  };
}