Material MkDocs crashes if both mkdocs-section-index and mkdocs-static-i18n plugins are used during running mkdocs serve

Description

When using Material MkDocs theme in combination with both the mkdocs-section-index and mkdocs-static-i18n plugins during running the server using mkdocs serve, Material MkDocs theme crashes and displays an error message.

Steps to Reproduce

Install Material MkDocs theme, mkdocs-section-index plugin, and mkdocs-static-i18n plugin via pip. Here is a list of currently installed pacages:

mkdocs                     1.4.2
mkdocs-ezlinks-plugin      0.1.14
mkdocs-material            9.1.5
mkdocs-material-extensions 1.1.1
mkdocs-section-index       0.3.5
mkdocs-static-i18n         0.56

Create a new MkDocs project and add the following to your mkdocs.yml configuration file:

mkdocs.yml

``` site_name: My Docs nav: - Main: index.md - Second: second.md - Third: - /third/index.md - Sub1: third/sub1.md - Sub2: third/sub2.md - Forth: forth.md extra: alternate: - name: English link: en/ lang: en - name: Français link: fr/ lang: fr theme: name: material palette: scheme: slate features: - navigation.tabs - navigation.tabs.sticky markdown_extensions: - attr_list - toc: permalink: ⚓︎ slugify: !!python/object/apply:pymdownx.slugs.slugify kwds: case: none plugins: - search - ezlinks - section-index - i18n: default_language: en docs_structure: folder languages: en: name: English fr: name: Français nav_translations: en: fr: ```

Create next structure of dirs and files

The scaffold of the site structure

``` . ├── docs │ ├── en │ │ ├── forth.md │ │ ├── index.md │ │ ├── second.md │ │ └── third │ │ ├── index.md │ │ ├── sub1.md │ │ └── sub2.md │ └── fr │ ├── forth.md │ ├── index.md │ ├── second.md │ └── third │ ├── index.md │ ├── sub1.md │ └── sub2.md └── mkdocs.yml 6 directories, 13 files ```

Start the development server by running mkdocs serve
Observe the error message displayed in the terminal

Crash log

```log INFO - Building en documentation Traceback (most recent call last): File "/Users/ahm/Documents/github/mkdocs-test/venv/bin/mkdocs", line 8, in sys.exit(cli()) ^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/click/core.py", line 1130, in __call__ return self.main(*args, **kwargs) ^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/click/core.py", line 1055, in main rv = self.invoke(ctx) ^^^^^^^^^^^^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/click/core.py", line 1657, in invoke return _process_result(sub_ctx.command.invoke(sub_ctx)) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/click/core.py", line 1404, in invoke return ctx.invoke(self.callback, **ctx.params) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/click/core.py", line 760, in invoke return __callback(*args, **kwargs) ^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs/__main__.py", line 234, in serve_command serve.serve(dev_addr=dev_addr, livereload=livereload, watch=watch, **kwargs) File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs/commands/serve.py", line 116, in serve server.serve() File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs/livereload/__init__.py", line 162, in serve self._build_loop() File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs/livereload/__init__.py", line 184, in _build_loop func() File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs/commands/serve.py", line 76, in builder build(config, live_server=live_server, dirty=dirty) File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs/commands/build.py", line 332, in build config.plugins.run_event('post_build', config=config) File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs/plugins.py", line 522, in run_event result = method(**kwargs) ^^^^^^^^^^^^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs_static_i18n/plugin.py", line 604, in on_post_build files.add_files_from_theme(env, config) File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/mkdocs/structure/files.py", line 122, in add_files_from_theme for path in env.list_templates(filter_func=filter): ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/jinja2/environment.py", line 914, in list_templates names = self.loader.list_templates() ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/ahm/Documents/github/mkdocs-test/venv/lib/python3.11/site-packages/jinja2/loaders.py", line 105, in list_templates raise TypeError("this loader cannot iterate over all templates") TypeError: this loader cannot iterate over all templates ```

Expected Results

The MkDocs site should load successfully, and the mkdocs-section-index and mkdocs-static-i18n plugins should function as expected.

Actual Results

The Material MkDocs theme crashes and displays an error message.

oprypin / mkdocs-section-index