Variable "lang" not found in context

[fyang93]

Bug Report

Variable "lang" is sometimes unavailable.

Environment

ArchLinux

Zola version: 0.10.0

Expected Behavior

First, I have a templates/index.html file where a title block <title>{% block title %}{% endblock title %}</title> is defined in the header.

Another file templates/tags/list.html extends index.html and overwrite the title block with {% block title %}{{ config.extra.tags[lang] }}{% endblock title %}.

Hopefully, the title will be adjusted to the current language.

Current Behavior

Failed to build the site
Error: Failed to render a list of tags page.
Reason: Failed to render 'tags/list.html'
Reason: Variable config.extra.tags[lang] can not be evaluated because: Variable lang not found in context while rendering 'tags/list.html'

Step to reproduce

Please refer to the Expected Behavior part.
And I have the following config in my config.toml file.

[extra.tags]
en="Tags"
zh="标签"
jp="タグ"

If you find it is hard to reproduce I could provide a minimal example later.

[Keats]

Looks like the taxonomy list template doesn't get lang like it should