Add missing locales and fix access to public pages

app/views/application/_breadcrumbs_and_title.html.slim

@@ -5,9 +5,9 @@
     - if object
       - current_element = object
   - else
-    - root_element = link_to_if(policy(model).index?, model.model_name.human(count: 2), send(:"#{model.model_name.collection}_path"))
+    - root_element = link_to_if(@current_user && policy(model).index?, model.model_name.human(count: 2), send(:"#{model.model_name.collection}_path"))
     - if object
-      - current_element = link_to_if(policy(object).show?, object, send(:"#{model.model_name.singular}_path", object))
+      - current_element = link_to_if(@current_user && policy(object).show?, object, send(:"#{model.model_name.singular}_path", object))
   - if I18n.translation_present?("shared.#{params[:action]}")
     - active_action = t("shared.#{params[:action]}")
   - else

app/views/exercises/external_users/statistics.html.slim

@@ -1,4 +1,4 @@
-h1 = "#{@exercise} (external user #{@external_user})"
+h1 = "#{@exercise} (external user #{link_to_if(policy(@external_user).show?, @external_user.displayname, @external_user)})"
 - current_submission = @submissions.first
 - if current_submission
   - initial_files = current_submission.files.to_a