如果没办法指定一个国家的语言，那么就指定语言。
Resource
- https://www.seozac.com/en-seo/hreflang-tag/
- https://developers.google.com/search/docs/advanced/crawling/localized-versions?visit_id=637617388336191859-489773827&rd=1
- https://searchengineland.com/the-ultimate-guide-to-multilingual-and-multiregional-seo-157838
- https://developers.google.com/search/blog/2013/04/x-default-hreflang-for-international-pages
- https://www.wangwanghere.com/zh/hreflang-intro
- https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes
- https://developers.google.com/search/docs/advanced/crawling/localized-versions#language-codes