website/_includes/vars.html

{% capture __vars %}
{% assign vars_url_parts = page.url | split: "/" | shift %}
{% assign vars_url_language = vars_url_parts[1] %}
{% assign vars_url_relative = vars_url_parts | shift | shift | join: "/" | replace: ".html", "" %}
{% assign vars_temp_matched_languages = site.data.languages | where: "tag", vars_url_language %}
{% assign vars_active_language = vars_temp_matched_languages[0] %}

{% unless vars_active_language %}
  {% assign vars_active_language = site.data.languages[0] %}
  {% assign vars_production_url_base_language = "" %}
{% else %}
  {% assign vars_production_url_base_language = "/" | append: vars_active_language.tag %}
{% endunless %}

{% assign i18n = site.data.i18n[vars_active_language.tag] %}

{% if jekyll.environment == "development" %}
  {% assign url_base = site.baseurl | append: "/lang/" | append: vars_active_language.tag %}
{% else %}
  {% assign url_base = site.baseurl | append: vars_production_url_base_language %}
{% endif %}
{% endcapture %}