feat: support server-side i18n integration

[kazupon]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR is feature PR of @intlify/h3 integration for nuxt i18n, and experimental feature.
I will also add docs.

we will consider some stuff the following:

• locale messages (i18n resources) will be able to use nuxt i18n options as much as possible
  • set the defineI18nMiddleware in the initialization of the nitro plugin
  • but, setting up all locale messages in the nitro plugin can have a performance impact, so consider lazy loading (we should load the locale when it is detected by the locale detector).
• server-side locale detection is done by a module that exports a user-defined locale detector function to the experimental.localeDetector option in the nuxt i18n config.
  • see about detauls for how to customize for locale detection: https://github.com/intlify/h3#%EF%B8%8F-custom-locale-detection
  • Ideally, it would be useful if locale detection could be seamlessly integrated with the nuxt i18n routing strategy and detect browserlanguage option. but, we don’t know use cases of server-side i18n, the first implementation allows users to customize locale detection on their own.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[kazupon]

This PR is still WIP.

[nuxt-studio]

✅ Live Preview ready!

Name	Edit	Preview	Latest Commit
i18n	Edit on Studio ↗︎	View Live Preview	cecac24

[BobbieGoede]

Nice, it looks great!

Only some small fixes/changes for the docs, other than that it looks like it can be merged 💪

[kazupon]

@BobbieGoede
Thanks for your review!
I'll merge this PR!