New Features 
Vue I18n v9 offers not only Vue 3 support, but this version also is included new features.
Message format syntax 
- See the Literal interpolation
 
Message functions 
- See the Linked messages
 - See the Pluralization
 
Composition API 
See the Composition API advanced section
Translation Component 
Support for plural prop. You can specify the number of messages to be pluralized.
The below example:
html
<template>
  <i18n-t keypath="message.plural" :plural="count">
    <template #n>
      <b>{{ count }}</b>
    </template>
  </i18n-t>
</template>
<script>
import { useI18n } from 'vue-i18n'
export default {
  setup() {
    const { t } = useI18n({
      locale: 'en',
      messages: {
        en: {
          message: {
            plural: 'no bananas | {n} banana | {n} bananas'
          }
        }
      }
    })
    const count = ref(0)
    return { count, t }
  }
}
</script>DatetimeFormat Component 
For Datetime localization, since Vue I18n v9, we also offer the DatetimeFormat component like the NumberFormat component.
See the Datetime localization custom formatting
i18n Custom Block 
- See the 
globalattribute