Dynamic nav in Jekyll (using a _data yml)

Question

This is very annoying. I tried to switch from a static to a dynamic nav in Jekyll, but now I am no longer able to assign a class to a link based on its url.

here how it was.

<nav class="site-nav">
               <a href="{{ site.baseurl }}/about/" class="{% if page.url == '/about/' %}active{% endif %}">About</a>
                <a href="{{ site.baseurl }}/archive/" class="{% if page.url == '/archive/' %}active{% endif %}">Archive</a>
                <a href="{{ site.baseurl }}/resources/" class="{% if page.url == '/resources/' %}active{% endif %}">Resources</a>
                <a href="{{ site.baseurl }}/books/" class="{% if page.url == '/books/' %}active{% endif %}">Books</a>
                <a href="{{ site.baseurl }}/subscribe/" class="{% if page.url == '/subscribe/' %}active{% endif %}">Subscribe</a>
                <a href="{{ site.baseurl }}/sample/" class="{% if page.url == '/sample/' %}active{% endif %}">sample</a>
  </nav>

It worked. Then, I changed it to

<nav>
          {% for menu in site.data.navigation[page.lang] %}
          <a href="{{site.baseurl}}{{ menu[1].url }}" class="{% if page.url == '{{ menu[1].url | prepand: site.baseurl }}' %}active{% endif %}">{{ menu[1].title }}</a>
          {% endfor %}
</nav>

Now it doesn't work. Any idea? The goal is to check the page.url against the nav menu url (menu[1].url) and if its identical apply the class "active". menu[1].url refers to content of _data/navigation, a yml file with menu list for two different nav based on page.lang.

the data file looks like this:

en:
  about:
    title: "about"
    url: "/about/"
  archive:
    title: "archive"
    url: "/archive/"
  resources:
    title: "resources"
    url: "/resources/"
  books:
    title: "books"
    url: "/books/"
  sample:
    title: "sample"
    url: "/sample/"

it:
  about:
    title: "about"
    url: "/about/"
  archive:
    title: "archive"
    url: "/archive/"
  resources:
    title: "resources"
    url: "/resources/"
  books:
    title: "books"
    url: "/books/"
  sample:
    title: "sample"
    url: "/sample/"

Answer 1

Here is the way I achieve this.

Files architecture

All posts and pages in an en or fr folder

--fr
   |--_posts
   |--about.html
   |--...
--en
   |--_posts
   |--about.html
   |--...

Lang configuration

In _config.yml add :

defaults:
# default lang is set to en
  -
    scope:
      path: ""
    values:
      lang: "en"
# lang is set to fr in the fr folder      
  -
    scope:
      path: "fr"
    values:
      lang: "fr"

Main navigation

In order to sort my page in the navigation bar, I've added a weight variable in pages front matter.

---
...
weight: 10
---

The code will generate navigation depending on current page lang.

<nav>
{% assign pages = site.pages | where: 'lang', page.lang | sort: 'weight' %}
{% for p in pages %}
  {% if p.title %}
    <a {% if p.url == page.url %} class="active"{% endif %} href="{{ site.baseurl }}{{ p.url }}">
      {{ p.title }}
    </a>
  {% endif %}
{% endfor %}
</nav>