<% @plans.each do |plan| %>
  <div class="sub-nav-item">
    <%= link_to plan.title, gobierto_plans_plan_path(id: plan.slug) %>
  </div>
<% end %>

<% current_site.plans.each do |plan| %>
  <div class="sub-nav-item">
    <%= link_to plan.title, gobierto_plans_plan_path(id: plan.slug) %>
  </div>
<% end %>

Modify navigation.sub plans with current_site.plans
Modify navigation.sub plans with current_site.plans
