Fixes the culturerequest.interceptor so that it works in tests (and so circular deps aren't caused), internalizes ClientCulture and makes it a little less error prone.

src/Umbraco.Web.UI.Client/src/common/interceptors/culturerequest.interceptor.js

@@ -3,23 +3,29 @@
 
     /**
      * Used to set the current client culture on all requests API requests
-     * @param {any} $q
      * @param {any} $routeParams
      */
-    function cultureRequestInterceptor($q, $routeParams) {
+    function cultureRequestInterceptor($injector) {
         return {
             //dealing with requests:
             'request': function (config) {
+
                 if (!Umbraco.Sys.ServerVariables.umbracoSettings.umbracoPath) {
                     // no settings available, we're probably on the login screen
                     return config;
                 }
+
                 if (!config.url.match(RegExp(Umbraco.Sys.ServerVariables.umbracoSettings.umbracoPath + "\/backoffice\/", "i"))) {
                     // it's not an API request, no handling
                     return config;
                 }
-                // it's an API request, add the current client culture as a header value
-                config.headers["X-UMB-CULTURE"] = $routeParams.cculture ? $routeParams.cculture : $routeParams.mculture;
+
+                var $routeParams = $injector.get("$routeParams");
+                if ($routeParams) {
+                    // it's an API request, add the current client culture as a header value
+                    config.headers["X-UMB-CULTURE"] = $routeParams.cculture ? $routeParams.cculture : $routeParams.mculture;
+                }
+                
                 return config;
             }
         };

src/Umbraco.Web/WebApi/HttpRequestMessageExtensions.cs

@@ -161,9 +161,9 @@ namespace Umbraco.Web.WebApi
             return msg;
         }
 
-        public static string ClientCulture(this HttpRequestMessage request)
+        internal static string ClientCulture(this HttpRequestMessage request)
         {
-            return request.Headers.Contains("X-UMB-CULTURE") ? request.Headers.GetValues("X-UMB-CULTURE").First() : null;
+            return request.Headers.TryGetValues("X-UMB-CULTURE", out var values) ? values.FirstOrDefault() : null;
         }
     }