{%comment%} check for the presence of the path in an array of paths. {%endcomment%}

{% for block in site.data.map %}
{% for item in block[page.lang] %}
{% if item == page.path %}
{% for trans in block %}
{% assign trans_path = trans[1] %}

{% assign posts = site.posts | where:"path",trans_path %} 
{% for item in posts %}
<link rel="alternate" hreflang="{{item.lang}}" href="{{item.url|absolute_url}}" />
{% endfor %}

{% assign pages = site.pages | where:"path",trans_path %} 
{% for item in pages %}
<link rel="alternate" hreflang="{{item.lang}}" href="{{item.url|absolute_url}}" />
{% endfor %}
{% endfor %}
{% endif %}
{% endfor %}
{% endfor %}