Anyone using vue3 + js for i18n lazy loading translation?

I don't really get into the example here https://vue-i18n.intlify.dev/guide/advanced/lazy.html. Is there any example for this?

I am getting undefined locale, when i set exactly same as the example. May i know what's wrong or anything i missed?

in my main.js

import { setupI18n as i18n } from '@/i18n'
const app = createApp(App)
  .use(i18n)

in my i18n.js

import { nextTick } from 'vue'
import { createI18n } from 'vue-i18n'

export const SUPPORT_LOCALES = ['en', 'ja']

export function setupI18n(options = { locale: 'en' }) {
  const i18n = createI18n(options)
  setI18nLanguage(i18n, options.locale)
  return i18n
}

export function setI18nLanguage(i18n, locale) {
  if (i18n.mode === 'legacy') {
    i18n.global.locale = locale
  } else {
    i18n.global.locale.value = locale
  }
  /**
   * NOTE:
   * If you need to specify the language setting for headers, such as the `fetch` API, set it here.
   * The following is an example for axios.
   *
   * axios.defaults.headers.common['Accept-Language'] = locale
   */
  document.querySelector('html').setAttribute('lang', locale)
}

export async function loadLocaleMessages(i18n, locale) {
  // load locale messages with dynamic import
  const messages = await import(
    /* webpackChunkName: "locale-[request]" */ `./locales/${locale}.json`
  )

  // set locale and locale message
  i18n.global.setLocaleMessage(locale, messages.default)

  return nextTick()
}