fix(i8n): compatibility with og:locale

[curbengh]

PR Checklist

• The commit message follows our guidelines.
• Tests for the changes was maked (for bug fixes / features).
  • Muse | Mist have been tested.
  • Pisces | Gemini have been tested.
• Docs in NexT website have been added / updated (for features).

PR Type

• Bugfix.
• Feature.
• Code style update (formatting, local variables).
• Refactoring (no functional changes, no api changes).
• Build related changes.
• CI related changes.
• Documentation content changes.
• Other... Please describe:

What is the current behavior?

Issue resolved: N/A

What is the new behavior?

• Screenshots with this changes: N/A
• Link to demo site with this changes: N/A

How to use?

In Hexo _config.yml:

language: en-US

Does this PR introduce a breaking change?

• Yes.
• No.

Description

A change introduced in hexojs/hexo#3808, og:locale Open Graph tag only accepts "language_TERRITORY" format.

Since "language_TERRITORY" breaks multilingual support, user should instead use "language-TERRITORY" format which is automatically transformed to "language_TERRITORY" in open_graph() helper.

However, "language-TERRITORY" still breaks multilingual support for non-ZH users, this PR fixes that.

See official list (by Facebook; Hexo only checks the length, not the value itself) of supported locales.

[welcome]

Thanks so much for opening your first PR here!

[curbengh]

A fix has been created in the upstream (hexojs/hexo#3921) to minimize breaking change. Despite that, I still think this PR is necessary.

[CLAassistant]

All committers have signed the CLA.