Incompatibility between mkdocs-git-revision-date-localized-plugin>=1.4.0 and mkdocs-static-i18n

[SimonSAMPERE]

I don't know if it's link to #86 but I have an MkDocs project using mkdocs-git-revision-date-localized-plugin and mkdocs-static-i18n. To support Brazilian Portuguese I have a folder doc/pt-BR and since 1.4.0 of mkdocs-git-revision-date-localized-plugin an error is raised trying to build (or serve loccaly) my project : ERROR - Error reading page 'pt-BR/index.md': expected only letters, got 'pt-br'

Full info below :

INFO    -  Building documentation...
INFO    -  mkdocs_static_i18n: Building 'fr' documentation to directory: %userprofile%\AppData\Local\Temp\mkdocs_ujfattiv
INFO    -  mkdocs_static_i18n: Adding 'fr' to the 'material/search' plugin 'lang' option
INFO    -  mkdocs_static_i18n: Adding 'es' to the 'material/search' plugin 'lang' option
INFO    -  mkdocs_static_i18n: Overriding 'fr' config 'site_name' with 'Plugin QGIS'
INFO    -  Cleaning site directory
INFO    -  mkdocs_static_i18n: Translated 27 navigation elements to 'fr'
INFO    -  mkdocs_static_i18n: Building 'en' documentation to directory: %userprofile%\AppData\Local\Temp\mkdocs_ujfattiv\en
INFO    -  mkdocs_static_i18n: Overriding 'en' config 'site_name' with 'QGIS Plugin'
INFO    -  mkdocs_static_i18n: Building 'fr' documentation to directory: %userprofile%\AppData\Local\Temp\mkdocs_ujfattiv
INFO    -  mkdocs_static_i18n: Overriding 'fr' config 'site_name' with 'Plugin QGIS'
INFO    -  mkdocs_static_i18n: Translated 27 navigation elements to 'fr'
INFO    -  mkdocs_static_i18n: Building 'es' documentation to directory: %userprofile%\AppData\Local\Temp\mkdocs_ujfattiv\es
INFO    -  mkdocs_static_i18n: Overriding 'es' config 'site_name' with 'Complemento QGIS'
INFO    -  mkdocs_static_i18n: Translated 27 navigation elements to 'es'
INFO    -  mkdocs_static_i18n: Building 'pt-BR' documentation to directory: %userprofile%\AppData\Local\Temp\mkdocs_ujfattiv\pt-BR
INFO    -  mkdocs_static_i18n: Language 'pt-BR' is not supported by lunr.js, not setting it in the 'plugins.search.lang' option
INFO    -  mkdocs_static_i18n: Overriding 'pt-BR' config 'site_name' with 'Complemento QGIS'
INFO    -  mkdocs_static_i18n: Translated 27 navigation elements to 'pt-BR'
ERROR   -  Error reading page 'pt-BR/index.md': expected only letters, got 'pt-br'
Traceback (most recent call last):
  File "C:\Program Files\Python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Program Files\Python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\Scripts\mkdocs.exe\__main__.py", line 7, in <module>
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\click\core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\click\core.py", line 1078, in main
    rv = self.invoke(ctx)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\click\core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\click\core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\click\core.py", line 783, in invoke
    return __callback(*args, **kwargs)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\__main__.py", line 272, in serve_command
    serve.serve(**kwargs)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\commands\serve.py", line 85, in serve
    builder(config)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\commands\serve.py", line 67, in builder
    build(config, serve_url=None if is_clean else serve_url, dirty=is_dirty)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\commands\build.py", line 347, in build
    config.plugins.on_post_build(config=config)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\plugins.py", line 602, in on_post_build
    return self.run_event('post_build', config=config)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\plugins.py", line 568, in run_event
    result = method(**kwargs)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs_static_i18n\plugin.py", line 253, in on_post_build
    build(config, dirty=dirty)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\commands\build.py", line 310, in build
    _populate_page(file.page, config, files, dirty)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\commands\build.py", line 163, in _populate_page
    page.markdown = config.plugins.on_page_markdown(
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\plugins.py", line 635, in on_page_markdown
    return self.run_event('page_markdown', markdown, page=page, config=config, files=files)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs\plugins.py", line 566, in run_event
    result = method(item, **kwargs)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs_git_revision_date_localized_plugin\plugin.py", line 245, in on_page_markdown
    revision_dates = self.util.get_date_formats_for_timestamp(
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs_git_revision_date_localized_plugin\util.py", line 216, in get_date_formats_for_timestamp
    date_formats = get_date_formats(
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\mkdocs_git_revision_date_localized_plugin\dates.py", line 29, in get_date_formats
    "date": format_date(loc_revision_date, format="long", locale=locale),
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\babel\dates.py", line 681, in format_date
    locale = Locale.parse(locale)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\babel\core.py", line 334, in parse
    parts = parse_locale(identifier, sep=sep)
  File "%userprofile%\Documents\GitHub\doc\doc-plugin-qgis\.venv\lib\site-packages\babel\core.py", line 1246, in parse_locale
    raise ValueError(f"expected only letters, got {lang!r}")
ValueError: expected only letters, got 'pt-br'