This mkdocs plugin is meant to be used with:

• mkdocs-material
• mike for multiple versions of your documentation
• multi-language documentation

The code in mkdocs-material that renders the version selection dropdown in the header dynamically requests versions.json relative to the page's base_url. This works well normally, but when you try to add multiple languages, things start to get a bit tricky.

I've set up my project documentation inside my repo like this:

.
├─ config/
│    ├─ en/
│    │  └─ mkdocs.yml
│    ├─ nl/
│    │  └─ mkdocs.yml
│    ├─ .../
│
├─ content/
│    ├─ en/
│    │   ├─ index.md 
│    │   └─ ...
│    └─ nl/
│        ├─ index.md 
│        └─ ,,,
│
├─ generated/
│    ├─ branch
│    │  ├─ en/
│    │  └─ nl/
│    └─ index.html
│
└─ ...

Each language has its own mkdocs.yml. Each is configured like this (only showing relevant parts, using en as an example):

docs_dir: '../../content/en'
site_dir: '../../generated/branch/en'
theme:
  language: en
extra:
  version:
    provider: mike
  alternate:
  - name: English
    link: en
    lang: en

plugins:
- modify-base-url:
    prefix: '../'

All languages are individually generated into docs/generated/branch/$LANGUAGE

There is a separate mkdocs.yml for mike to support versioning. There is really only one key, required setting, that tells mike to use what we previously generated:

docs_dir: generated/branch

When you run mike deploy VERSION from within the docs directory, it combines all the generated documentation for all the languages into a single version. There is also a static index.html file in docs/generated/branch that redirects initial requests to a default language.

Given a URL such as docs.kcp.io/kcp/main/en, when visiting index.html, its base_url is normally . because we told mkdocs to generate directly into the en directory. What's unique about this situation is that mkdocs thinks that one level up from en should be where versions.json lives. But it's actually up one more level, at docs.kcp.io/kcp/versions.json because of our configuration.

And this is why this plugin exists. We need to adjust the base_url to move it up one more level, so instead of it being . for docs.kcp.io/kcp/main/en/index.html, it's actually ... Now, when mkdocs-material requests base_url/../versions.json, that becomes ../../versions.json, which is really docs.kcp.io/kcp/versions.json.