[Validation]: add localization tests + docs + DI package for tests

- 3 new tests: default (no localizer), with TestLocalizer, null fallback
- Docs: localization section in ASP.NET integration page
- Test project gets Microsoft.Extensions.DependencyInjection reference

70 tests pass.

Author: MistyKuu

docs/src/content/docs/packages/validation/aspnet.md

@@ -88,6 +88,44 @@ app.MapPost("/api/users", (UserDto dto) =>
 
 > Note: `.WithValidation()` calls `Validate()` with no ruleset (validates all). For selective validation, call manually in the handler.
 
+## Localization (i18n)
+
+Register an `IValidationLocalizer` in DI — all generated messages pass through it automatically:
+
+```csharp
+// 1. Implement the interface:
+public class PolishLocalizer : IValidationLocalizer
+{
+    private readonly IStringLocalizer<SharedResources> _loc;
+    
+    public PolishLocalizer(IStringLocalizer<SharedResources> loc) => _loc = loc;
+
+    public string? GetMessage(string property, string defaultMessage)
+    {
+        var localized = _loc[defaultMessage];
+        return localized.ResourceNotFound ? null : localized.Value;
+    }
+}
+
+// 2. Register in DI:
+builder.Services.AddSingleton<IValidationLocalizer, PolishLocalizer>();
+
+// 3. Call once at startup:
+app.Services.ConfigureValidation();
+```
+
+That's it. `.WithValidation()` auto-resolves the localizer. Manual `Validate()` also uses it (resolved from the static `ValidationServiceProvider`).
+
+Without `IValidationLocalizer` in DI → default English messages (zero breaking change).
+
+## Setup
+
+```csharp
+var app = builder.Build();
+app.Services.ConfigureValidation();  // bridges DI → validation runtime (for localization)
+app.Services.ConfigureAop();         // if using [Log]/[Trace] etc.
+```
+
 ## Requirements
 
 `.WithValidation()` is auto-generated when your project references `Microsoft.AspNetCore.Http` (Web SDK projects). Non-web projects (class libraries, test projects) don't get this extension method — it's conditionally emitted.

packages/ZibStack.NET.Validation/tests/ZibStack.NET.Validation.Tests/ValidationTests.cs

@@ -1,3 +1,4 @@
+using Microsoft.Extensions.DependencyInjection;
 using Xunit;
 using ZibStack.NET.Validation;
 
@@ -698,4 +699,74 @@ public void RuleSet_ValidForCreate_NoError()
         var result = obj.Validate(null, "Create");
         Assert.True(result.IsValid);
     }
+
+    // ── Localization ─────────────────────────────────────────────────
+
+    [Fact]
+    public void Localization_WithoutLocalizer_ReturnsDefaultMessage()
+    {
+        // No localizer registered → default English messages
+        ValidationServiceProvider.ServiceProvider = null;
+        var obj = new CascadeTest { Name = "" };
+        var result = obj.Validate();
+
+        Assert.Contains(result.Errors, e => e.Contains("is required"));
+    }
+
+    [Fact]
+    public void Localization_WithLocalizer_ReturnsLocalizedMessage()
+    {
+        // Register a test localizer
+        var services = new Microsoft.Extensions.DependencyInjection.ServiceCollection();
+        services.AddSingleton<IValidationLocalizer>(new TestLocalizer());
+        var sp = services.BuildServiceProvider();
+        ValidationServiceProvider.ServiceProvider = sp;
+
+        try
+        {
+            var obj = new CascadeTest { Name = "" };
+            var result = obj.Validate();
+
+            Assert.Contains(result.Errors, e => e.Contains("LOCALIZED:"));
+        }
+        finally
+        {
+            ValidationServiceProvider.ServiceProvider = null;
+        }
+    }
+
+    [Fact]
+    public void Localization_ReturnsNull_FallsBackToDefault()
+    {
+        var services = new Microsoft.Extensions.DependencyInjection.ServiceCollection();
+        services.AddSingleton<IValidationLocalizer>(new NullLocalizer());
+        var sp = services.BuildServiceProvider();
+        ValidationServiceProvider.ServiceProvider = sp;
+
+        try
+        {
+            var obj = new CascadeTest { Name = "" };
+            var result = obj.Validate();
+
+            // NullLocalizer returns null → falls back to default
+            Assert.Contains(result.Errors, e => e.Contains("is required"));
+        }
+        finally
+        {
+            ValidationServiceProvider.ServiceProvider = null;
+        }
+    }
+}
+
+// Test localizers
+internal class TestLocalizer : IValidationLocalizer
+{
+    public string? GetMessage(string property, string defaultMessage)
+        => $"LOCALIZED: {defaultMessage}";
+}
+
+internal class NullLocalizer : IValidationLocalizer
+{
+    public string? GetMessage(string property, string defaultMessage)
+        => null; // fall back to default
 }

packages/ZibStack.NET.Validation/tests/ZibStack.NET.Validation.Tests/ZibStack.NET.Validation.Tests.csproj

@@ -9,6 +9,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="xunit" Version="2.9.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />