     locale: 'ja',
        fallbackFormat: true, // enable, fallback to locale message key
        messages: {
          // `hello, {name}` key is nothing in `messages` option
          en: {},
          ja: {}
        }
      })

      const app = createApp({
        setup() {
          const { t } = useI18n()

          // Something to do ...
          //

          return { t }
        }
      })
      app.use(i18n)
      app.mount('#app')
    </script>
  </body>
</html>
