<% @taxons = @taxon && @taxon.parent ? @taxon.parent.children : Spree::Taxon.roots %>
<%= form_tag spree.products_path, :method => :get, class: "navbar-form" do %>
<div class="form-group">
  <% cache(cache_key_for_taxons) do %>
    <%= select_tag :taxon,
          options_for_select([[Spree.t(:all_departments), '']] +
                                @taxons.map {|t| [t.name, t.id]},
                                @taxon ? @taxon.id : params[:taxon]), 'aria-label' => 'Taxon', class: "form-control" %>
  <% end %>
</div>
<div class="form-group">
  <%= search_field_tag :keywords, params[:keywords], :placeholder => Spree.t(:search), class: "form-control" %>
</div>
<%= submit_tag Spree.t(:search), :name => nil, class: "btn btn-success" %>
<% end %>

<% @taxons = @taxon && @taxon.parent ? @taxon.parent.children : Spree::Taxon.roots %>
<%= form_tag spree.products_path, :method => :get, class: "navbar-form" do %>
<div class="form-group">
  <% cache([I18n.locale, cache_key_for_taxons]) do %>
    <%= select_tag :taxon,
          options_for_select([[Spree.t(:all_departments), '']] +
                                @taxons.map {|t| [t.name, t.id]},
                                @taxon ? @taxon.id : params[:taxon]), 'aria-label' => 'Taxon', class: "form-control" %>
  <% end %>
</div>
<div class="form-group">
  <%= search_field_tag :keywords, params[:keywords], :placeholder => Spree.t(:search), class: "form-control" %>
</div>
<%= submit_tag Spree.t(:search), :name => nil, class: "btn btn-success" %>
<% end %>

Add locale to cache method in search helper
Add locale to cache method in search helper
