Have you read the Contributing Guidelines on issues?

• I have read the Contributing Guidelines on issues.

Prerequisites

• I'm using the latest version of Docusaurus.
• I have tried the npm run clear or yarn clear command.
• I have tried rm -rf node_modules yarn.lock package-lock.json and re-installing packages.
• I have tried creating a repro with https://new.docusaurus.io.
• I have read the console error message carefully (if applicable).

Description

By the upgrade of the MDX plugin, the border of the document body and the footnotees has been changed from <hr> to the English-fixed heading. I couldn't find a way to change the language of the heading.

Some remark and related plugins can customize the "Footnotes" label by the option passed to mdast-util-to-hast.toHast.

https://github.com/remarkjs/remark-rehype#fields
https://github.com/remarkjs/remark-rehype#example-footnotes-in-languages-other-than-english
https://github.com/remarkjs/remark-html#options
https://github.com/syntax-tree/mdast-util-to-hast#footnotes
https://github.com/micromark/micromark-extension-gfm-footnote#label

Reproducible demo

WIP

Steps to reproduce

1. Set the language of your document as other than English
2. Add a footnote to a page in docs
3. docusaurus start
4. Open the page in your browser

Expected behavior

The footnote label is that in the language of your language (e.g. "脚注" in Japanese)

Actual behavior

Always "Footnotes" regardless of your language

Your environment

• Public source code: WIP
• Public site URL: WIP
• Docusaurus version used: 3.0.0
• Environment name and version (e.g. Chrome 89, Node.js 16.4): Firefox
• Operating system and version (e.g. Ubuntu 20.04.2 LTS): Windows 11

Self-service

• I'd be willing to fix this bug myself.
  ↑ If easy to fix, but doesn't seem