Log whether the localization resource is found or not

src/Localization/Localization/src/ResourceManagerStringLocalizer.cs

@@ -166,16 +166,26 @@
 
         if (_missingManifestCache.ContainsKey(cacheKey))
         {
+            Log.ResourceNotFound(_logger, name);
+
             return null;
         }
 
         try
         {
-            return _resourceManager.GetString(name, culture);
+            var value = _resourceManager.GetString(name, culture);
+
+            if (name != value)
+            {
+                Log.ResourceNotFound(_logger, name);
+            }
+
+            return value;
         }
         catch (MissingManifestResourceException)
         {
             _missingManifestCache.TryAdd(cacheKey, null);
+
             return null;
         }
     }
@@ -221,5 +231,8 @@
     {
         [LoggerMessage(1, LogLevel.Debug, $"{nameof(ResourceManagerStringLocalizer)} searched for '{{Key}}' in '{{LocationSearched}}' with culture '{{Culture}}'.", EventName = "SearchedLocation")]
         public static partial void SearchedLocation(ILogger logger, string key, string locationSearched, CultureInfo culture);
+
+        [LoggerMessage(2, LogLevel.Debug, $"A resource for '{{Key}}' with culture '{{Culture}}' was not found.", EventName = "ResourceNotFound")]
+        public static partial void ResourceNotFound(ILogger logger, string key);
     }
 }

src/Localization/Localization/test/Microsoft.Extensions.Localization.Tests/ResourceManagerStringLocalizerTest.cs

@@ -136,8 +136,10 @@ public void GetString_LogsLocationSearched()
         var value = localizer["a key!"];
 
         // Assert
-        var write = Assert.Single(Sink.Writes);
-        Assert.Equal("ResourceManagerStringLocalizer searched for 'a key!' in 'Resources.TestResource' with culture 'en-US'.", write.State.ToString());
+        var write = Sink.Writes;
+        Assert.Equal(2, write.Count);
+        Assert.Equal("ResourceManagerStringLocalizer searched for 'a key!' in 'Resources.TestResource' with culture 'en-US'.", write.ElementAt(0).State.ToString());
+        Assert.Equal("The resource with key 'a key!' is found.", write.ElementAt(1).State.ToString());
     }
 
     [Theory]