expressjs.com/_includes/bottom-navigation.html

{% assign current_menu = page.menu %}
{% assign current_lang = page.lang %}

{% if current_menu and current_lang %}

  {% assign all_pages_in_menu = site.pages | where: "menu", current_menu %}
  {% assign lang_specific_pages = all_pages_in_menu | where: "lang", current_lang %}
  
  {% assign sorted_pages = lang_specific_pages | sort: "order" %}

  {% for doc in sorted_pages %}
    {% if doc.path == page.path %}
      {% assign current_index = forloop.index0 %}
      {% break %}
    {% endif %}
  {% endfor %}

  {% if current_index != nil %}
    {% assign prev_index = current_index | minus: 1 %}
    {% if prev_index >= 0 %}
      {% assign prev_page = sorted_pages[prev_index] %}
    {% endif %}

    {% assign next_index = current_index | plus: 1 %}
    {% if next_index < sorted_pages.size %}
      {% assign next_page = sorted_pages[next_index] %}
    {% endif %}
  {% endif %}

  {% if prev_page or next_page %}
    <nav class="bottom-navigation" aria-label="Pagination">
      {% if prev_page %}
        <a href="{{ prev_page.url | relative_url }}" class="bottom-nav-prev">
          Previous: {{ prev_page.title }}
        </a>
      {% endif %}

      {% if next_page %}
        <a href="{{ next_page.url | relative_url }}" class="bottom-nav-next">
          Next: {{ next_page.title }}
        </a>
      {% endif %}
    </nav>
  {% endif %}

{% endif %}