support for vue-i18n v12

[kazupon]

Clear and concise description of the problem

requirement

vue-i18n v12 is going to ship the ESM only and drop legacy API. so we need to bundle it with unpluign-vue-i18n

• bundle vue-i18n that is extension is .js, not .mjs
• drop feature flags setting of legacy API

Suggested solution

N/A

Alternative

No response

Additional context

No response

Validations

• Read the Contributing Guidelines.
• Read the README
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.

[kazupon]

close
thanks @babu-ch contribution!

[babu-ch]

🎉
If you still have tasks, I will help you!