{% comment %}The variable already exists through the breadcrumb include:
{% assign doc_data = 'docs_' | append: site.active_lang %}
{% assign page_data = site.data[doc_data].by_title[page.title] %}
{%endcomment %}
{% if page_data.previous_url != '' %}← {{ page_data.previous_title }}{% endif %}{% if page_data.next_url != '' %}{{ page_data.next_title }} →{% endif %}