navbar: fix unkeyed strings

_i18n/en.yml

@@ -7,6 +7,7 @@ global:
   download: "Download"
   related_information: "Related Information"
   contrib: "This software may depend on or recommend non-free software."
+  theme: "Theme"
 aria:
   nav_toggle: "Toggle navigation"
 service_descriptions:

_includes/nav.html

@@ -126,7 +126,7 @@
         <details class="nav-details">
           <summary>
             <span class="nav-summary">
-              Services
+              {% t service_descriptions.services %}
               <span class="dropdown-toggle"></span>
             </span>
           </summary>
@@ -146,7 +146,7 @@
           {% t resources.sponsors %}
         </a>
         <span id="nav-switch-theme" class="nav-anchor">
-          Theme <span class="nav-theme-icon fas fa-fw"></span>
+          {% t global.theme %} <span class="nav-theme-icon fas fa-fw"></span>
         </span>
       </div>
     </div>