added a localization in docs

modules/docs/src/Volo.Docs.Domain/Volo/Docs/Localization/Domain/en.json

@@ -14,6 +14,7 @@
     "NoProjectWarning": "There are no projects yet!",
     "DocumentNotFound": "Oops, the requested document was not found!",
     "NavigationDocumentNotFound": "This version does not have a navigation document!",
-    "DocumentNotFoundInSelectedLanguage": "Document in the language you wanted is not found. Document in the default language is shown."
+    "DocumentNotFoundInSelectedLanguage": "Document in the language you wanted is not found. Document in the default language is shown.",
+    "FilterTopics": "Filter topics"
   }
 }

modules/docs/src/Volo.Docs.Web/Pages/Documents/Project/Index.cshtml

@@ -139,7 +139,7 @@
                                     <label class="input-group-text"><i class="fa fa-filter"></i></label>
                                 </div>
 
-                                <input class="form-control" type="search" placeholder="Filter topics" aria-label="Filter">
+                                <input class="form-control" type="search" placeholder="@L["FilterTopics"].Value" aria-label="Filter">
                             </div>
                         </div>
                     </div>