Refactor localization dictionary handling and improve test cases for split localization files

framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/VirtualFileLocalizationResourceContributorBase.cs

@@ -89,7 +89,7 @@ public abstract class VirtualFileLocalizationResourceContributorBase : ILocaliza
 
     private Dictionary<string, ILocalizationDictionary> CreateDictionaries()
     {
-        var dictionaries = new Dictionary<string, ILocalizationDictionary>();
+        var rawDictionaries = new Dictionary<string, Dictionary<string, LocalizedString>>();
 
         foreach (var file in _virtualFileProvider.GetDirectoryContents(_virtualPath)
                      .Where(f => !f.IsDirectory && CanParseFile(f))
@@ -102,20 +102,19 @@ public abstract class VirtualFileLocalizationResourceContributorBase : ILocaliza
                 continue;
             }
 
-            if (!dictionaries.ContainsKey(dictionary.CultureName))
+            if (!rawDictionaries.TryGetValue(dictionary.CultureName, out var raw))
             {
-                dictionaries[dictionary.CultureName] = dictionary;
-            }
-            else
-            {
-                var merged = new Dictionary<string, LocalizedString>();
-                dictionaries[dictionary.CultureName].Fill(merged);
-                dictionary.Fill(merged);
-                dictionaries[dictionary.CultureName] = new StaticLocalizationDictionary(dictionary.CultureName, merged);
+                raw = new Dictionary<string, LocalizedString>();
+                rawDictionaries[dictionary.CultureName] = raw;
             }
+
+            dictionary.Fill(raw);
         }
 
-        return dictionaries;
+        return rawDictionaries.ToDictionary(
+            kvp => kvp.Key,
+            kvp => (ILocalizationDictionary)new StaticLocalizationDictionary(kvp.Key, kvp.Value)
+        );
     }
 
     protected abstract bool CanParseFile(IFileInfo file);

framework/test/Volo.Abp.Localization.Tests/Volo/Abp/Localization/AbpStringLocalizerFactory_Tests.cs

@@ -93,7 +93,7 @@ public class AbpStringLocalizerFactory_Tests : AbpIntegratedTest<AbpLocalization
     }
 
     [Fact]
-    public void Should_Create_Resource_By_Name_FromSplitFiles()
+    public void Should_Create_Resource_By_Name_From_Split_Files()
     {
         using (CultureHelper.Use("en"))
         {

framework/test/Volo.Abp.Localization.Tests/Volo/Abp/Localization/JsonLocalizationDictionaryBuilder_Tests.cs

@@ -10,29 +10,25 @@ namespace Volo.Abp.Localization;
 public class JsonLocalizationDictionaryBuilder_Tests
 {
     [Fact]
-    public void JsonLocalizationDictionaryBuilder_Should_Handle_Duplicates()
+    public void Should_Use_Nested_Value_When_Flat_Key_Is_Defined_Before_Nested_Object()
     {
+        // When a flat key (e.g. "Foo__Bar") appears before a nested object (e.g. "Foo": {"Bar": ...}),
+        // the nested value wins because FlattenTexts processes keys in order and last-write wins.
         var input = """
             {
               "culture": "en",
               "texts": {
-                "ThisFieldIsRequired": "This field is required",
-                "MaxLenghtErrorMessage": "This field can be maximum of '{0}' chars",
-                "Enum:BookType.Undefined": "Undefined from ValidationResource",
-                "Enum:BookType.0": "Undefined with value 0 from ValidationResource",
-                "BookType.Adventure": "Adventure from ValidationResource",
-                "BookType.1": "Adventure with value 1 from ValidationResource",
-                "Biography": "Biography from ValidationResource",
-                "ThisFieldIsRequired": "This field is required again"
+                "DeepLocalizationKey__DeepKey": "FlatValue",
+                "DeepLocalizationKey": { "DeepKey": "NestedValue" }
               }
             }
             """;
 
         var localizationDictionary = JsonLocalizationDictionaryBuilder.BuildFromJsonString(input);
-        var localizationString = localizationDictionary.GetOrNull("ThisFieldIsRequired");
+        localizationDictionary.ShouldNotBeNull();
+        var localizationString = localizationDictionary.GetOrNull("DeepLocalizationKey__DeepKey");
         localizationString.ShouldNotBeNull();
-
-        localizationString.Value.ShouldBe("This field is required again");
+        localizationString.Value.ShouldBe("NestedValue");
     }
 
     [Fact]