Improve the way to set the default value of locales

_includes/related-posts.html

@@ -81,7 +81,7 @@
 {% if index_list.size > 0 %}
   <div id="related-posts" class="mt-5 mb-2 mb-sm-4">
     <h3 class="pt-2 mt-1 mb-4 ml-1"
-      data-toc-skip>{{ site.data.locales[site.lang].post.relate_posts | default: 'Further Reading' }}</h3>
+      data-toc-skip>{{ site.data.locales[lang].post.relate_posts }}</h3>
     <div class="card-deck mb-4">
     {% for entry in index_list %}
       {% assign index = entry | plus: 0 %}