Ecng.Localization 1.0.224

Ecng.Localization

A lightweight and flexible localization engine for .NET applications that provides centralized string resource management with support for multiple cultures and easy resource overrides.

Table of Contents

• Overview
• Key Features
• Installation
• Quick Start
• Core Concepts
• Usage Guide
• Advanced Scenarios
• Integration with .NET Attributes
• Best Practices
• API Reference

Overview

Ecng.Localization provides a simple yet powerful localization infrastructure that allows you to:

• Centralize all localizable strings in your application
• Support multiple languages and cultures
• Implement custom translation providers
• Integrate seamlessly with .NET data annotations
• Maintain type-safe resource keys

The library uses a provider pattern through the ILocalizer interface, making it easy to plug in custom localization strategies ranging from simple in-memory dictionaries to database-backed translation systems.

Key Features

• Pluggable Architecture: Implement custom localizers via ILocalizer interface
• Two Localization Modes: Translate by English text or by resource key
• Resource Type Support: Works with DisplayAttribute for declarative localization
• Extension Methods: Convenient string extension methods for inline localization
• Thread-Safe: Can be safely used in multi-threaded applications
• No External Dependencies: Minimal footprint with no third-party dependencies
• Fallback Behavior: Returns original text when translation is not found
• Type-Safe Keys: Const keys prevent typos in resource references

Installation

Add a reference to the Ecng.Localization project or NuGet package in your application:

<ItemGroup>
  <ProjectReference Include="path\to\Ecng.Localization.csproj" />
</ItemGroup>

Quick Start

Basic Usage

using Ecng.Localization;

// Use the default localizer (returns input as-is)
string text = "Hello".Localize();
Console.WriteLine(text); // Output: Hello

// Use predefined resource keys
string name = LocalizedStrings.Name;
Console.WriteLine(name); // Output: Name (in English by default)

Implementing Custom Localization

using Ecng.Localization;

// 1. Create a custom localizer
public class RussianLocalizer : ILocalizer
{
    private readonly Dictionary<string, string> _translations = new()
    {
        ["Name"] = "Имя",
        ["Warnings"] = "Предупреждения",
        ["Errors"] = "Ошибки",
        ["Info"] = "Информация"
    };

    public string Localize(string enStr)
    {
        // Translate by English text
        return _translations.GetValueOrDefault(enStr, enStr);
    }

    public string LocalizeByKey(string key)
    {
        // Translate by resource key
        return _translations.GetValueOrDefault(key, key);
    }
}

// 2. Register the localizer globally
LocalizedStrings.Localizer = new RussianLocalizer();

// 3. Use localized strings throughout your application
Console.WriteLine(LocalizedStrings.Name);      // Output: Имя
Console.WriteLine(LocalizedStrings.Warnings);  // Output: Предупреждения
Console.WriteLine("Name".Localize());          // Output: Имя

Core Concepts

ILocalizer Interface

The ILocalizer interface is the foundation of the localization system:

public interface ILocalizer
{
    /// <summary>
    /// Localizes a string by its English text.
    /// </summary>
    string Localize(string enStr);

    /// <summary>
    /// Localizes a string by its resource key.
    /// </summary>
    string LocalizeByKey(string key);
}

Two Translation Approaches:

1. Localize(enStr): Uses English text as the key. Good for dynamic strings.
2. LocalizeByKey(key): Uses a constant key. Better for compile-time safety.

LocalizedStrings Class

The static LocalizedStrings class provides:

• Global localizer instance via Localizer property
• Predefined resource keys (e.g., NameKey, IdKey, WarningsKey)
• Predefined localized string properties (e.g., Name, Id, Warnings)
• Extension methods for string localization

Default Behavior

By default, the library uses a null localizer that returns strings as-is:

// Default behavior (no translation)
"Hello".Localize();           // Returns: "Hello"
"MyKey".LocalizeByKey();      // Returns: "MyKey"
LocalizedStrings.Name;        // Returns: "Name"

Usage Guide

1. Using Predefined Resource Keys

The library provides predefined keys for common UI elements:

using Ecng.Localization;

// Logging-related resources
Console.WriteLine(LocalizedStrings.Inherited);    // "Inherited"
Console.WriteLine(LocalizedStrings.Verbose);      // "Verbose"
Console.WriteLine(LocalizedStrings.Debug);        // "Debug"
Console.WriteLine(LocalizedStrings.Info);         // "Info"
Console.WriteLine(LocalizedStrings.Warnings);     // "Warnings"
Console.WriteLine(LocalizedStrings.Errors);       // "Errors"
Console.WriteLine(LocalizedStrings.Off);          // "Off"

// General purpose resources
Console.WriteLine(LocalizedStrings.Id);           // "Id"
Console.WriteLine(LocalizedStrings.Name);         // "Name"
Console.WriteLine(LocalizedStrings.Logging);      // "Logging"
Console.WriteLine(LocalizedStrings.LogLevel);     // "LogLevel"

// Chart-related resources
Console.WriteLine(LocalizedStrings.Line2);        // "Line2"
Console.WriteLine(LocalizedStrings.Area);         // "Area"
Console.WriteLine(LocalizedStrings.Histogram);    // "Histogram"
Console.WriteLine(LocalizedStrings.Band);         // "Band"

2. Using String Extension Methods

Localize any string inline using extension methods:

using Ecng.Localization;

// Localize by English text
string message = "Connection established".Localize();

// Localize by key
string errorMsg = "ERROR_CONNECTION".LocalizeByKey();

// Use in string interpolation
Console.WriteLine($"Status: {"Active".Localize()}");

3. Implementing a Database-Backed Localizer

using Ecng.Localization;

public class DatabaseLocalizer : ILocalizer
{
    private readonly ITranslationRepository _repository;
    private readonly string _cultureCode;
    private readonly Dictionary<string, string> _cache;

    public DatabaseLocalizer(ITranslationRepository repository, string cultureCode)
    {
        _repository = repository;
        _cultureCode = cultureCode;
        _cache = new Dictionary<string, string>();
        LoadTranslations();
    }

    private void LoadTranslations()
    {
        // Load all translations for the current culture into cache
        var translations = _repository.GetTranslations(_cultureCode);
        foreach (var translation in translations)
        {
            _cache[translation.Key] = translation.Value;
        }
    }

    public string Localize(string enStr)
    {
        if (_cache.TryGetValue(enStr, out var translation))
            return translation;

        // Log missing translation for later addition
        _repository.LogMissingTranslation(enStr, _cultureCode);
        return enStr;
    }

    public string LocalizeByKey(string key)
    {
        return _cache.GetValueOrDefault(key, key);
    }
}

// Usage
var repository = new SqlTranslationRepository(connectionString);
LocalizedStrings.Localizer = new DatabaseLocalizer(repository, "ru-RU");

4. Implementing a Resource File Localizer

using Ecng.Localization;
using System.Resources;
using System.Globalization;

public class ResourceFileLocalizer : ILocalizer
{
    private readonly ResourceManager _resourceManager;
    private readonly CultureInfo _culture;

    public ResourceFileLocalizer(Type resourceType, CultureInfo culture)
    {
        _resourceManager = new ResourceManager(resourceType);
        _culture = culture;
    }

    public string Localize(string enStr)
    {
        try
        {
            // Try to get the resource using the English string as the key
            var result = _resourceManager.GetString(enStr, _culture);
            return result ?? enStr;
        }
        catch
        {
            return enStr;
        }
    }

    public string LocalizeByKey(string key)
    {
        try
        {
            var result = _resourceManager.GetString(key, _culture);
            return result ?? key;
        }
        catch
        {
            return key;
        }
    }
}

// Usage
LocalizedStrings.Localizer = new ResourceFileLocalizer(
    typeof(MyResources),
    new CultureInfo("fr-FR")
);

5. Culture-Aware Localizer with Fallback

using Ecng.Localization;
using System.Globalization;

public class MultiCultureLocalizer : ILocalizer
{
    private readonly Dictionary<string, Dictionary<string, string>> _translations;
    private CultureInfo _currentCulture;

    public MultiCultureLocalizer()
    {
        _translations = new Dictionary<string, Dictionary<string, string>>
        {
            ["en-US"] = new Dictionary<string, string>(),
            ["ru-RU"] = new Dictionary<string, string>
            {
                ["Name"] = "Имя",
                ["Errors"] = "Ошибки",
                ["Warnings"] = "Предупреждения"
            },
            ["de-DE"] = new Dictionary<string, string>
            {
                ["Name"] = "Name",
                ["Errors"] = "Fehler",
                ["Warnings"] = "Warnungen"
            }
        };

        _currentCulture = CultureInfo.CurrentUICulture;
    }

    public CultureInfo Culture
    {
        get => _currentCulture;
        set => _currentCulture = value ?? CultureInfo.InvariantCulture;
    }

    public string Localize(string enStr)
    {
        return LocalizeByKey(enStr);
    }

    public string LocalizeByKey(string key)
    {
        // Try exact culture match
        if (_translations.TryGetValue(_currentCulture.Name, out var cultureDict))
        {
            if (cultureDict.TryGetValue(key, out var translation))
                return translation;
        }

        // Try neutral culture (e.g., "ru" from "ru-RU")
        if (!_currentCulture.IsNeutralCulture)
        {
            var neutralCulture = _currentCulture.Parent.Name;
            if (_translations.TryGetValue(neutralCulture, out var neutralDict))
            {
                if (neutralDict.TryGetValue(key, out var translation))
                    return translation;
            }
        }

        // Fallback to English or return key
        if (_translations.TryGetValue("en-US", out var enDict))
        {
            if (enDict.TryGetValue(key, out var enTranslation))
                return enTranslation;
        }

        return key;
    }

    public void AddTranslation(string culture, string key, string value)
    {
        if (!_translations.ContainsKey(culture))
            _translations[culture] = new Dictionary<string, string>();

        _translations[culture][key] = value;
    }
}

// Usage
var localizer = new MultiCultureLocalizer();
localizer.Culture = new CultureInfo("ru-RU");
LocalizedStrings.Localizer = localizer;

Console.WriteLine(LocalizedStrings.Name);     // Output: Имя
Console.WriteLine(LocalizedStrings.Warnings); // Output: Предупреждения

Advanced Scenarios

Thread-Safe Localizer with Caching

using Ecng.Localization;
using System.Collections.Concurrent;

public class CachedLocalizer : ILocalizer
{
    private readonly ILocalizer _innerLocalizer;
    private readonly ConcurrentDictionary<string, string> _cache;
    private readonly int _maxCacheSize;

    public CachedLocalizer(ILocalizer innerLocalizer, int maxCacheSize = 1000)
    {
        _innerLocalizer = innerLocalizer;
        _cache = new ConcurrentDictionary<string, string>();
        _maxCacheSize = maxCacheSize;
    }

    public string Localize(string enStr)
    {
        return _cache.GetOrAdd(enStr, key =>
        {
            if (_cache.Count >= _maxCacheSize)
                _cache.Clear();
            return _innerLocalizer.Localize(key);
        });
    }

    public string LocalizeByKey(string key)
    {
        return _cache.GetOrAdd($"KEY_{key}", _ =>
        {
            if (_cache.Count >= _maxCacheSize)
                _cache.Clear();
            return _innerLocalizer.LocalizeByKey(key);
        });
    }

    public void ClearCache() => _cache.Clear();
}

Composite Localizer with Multiple Sources

using Ecng.Localization;

public class CompositeLocalizer : ILocalizer
{
    private readonly List<ILocalizer> _localizers;

    public CompositeLocalizer(params ILocalizer[] localizers)
    {
        _localizers = new List<ILocalizer>(localizers);
    }

    public string Localize(string enStr)
    {
        foreach (var localizer in _localizers)
        {
            var result = localizer.Localize(enStr);
            if (result != enStr)
                return result;
        }
        return enStr;
    }

    public string LocalizeByKey(string key)
    {
        foreach (var localizer in _localizers)
        {
            var result = localizer.LocalizeByKey(key);
            if (result != key)
                return result;
        }
        return key;
    }
}

// Usage: Try database first, then fall back to resource files
var dbLocalizer = new DatabaseLocalizer(repository, "ru-RU");
var fileLocalizer = new ResourceFileLocalizer(typeof(Resources), culture);
LocalizedStrings.Localizer = new CompositeLocalizer(dbLocalizer, fileLocalizer);

Logging Localizer (Debugging)

using Ecng.Localization;

public class LoggingLocalizer : ILocalizer
{
    private readonly ILocalizer _innerLocalizer;
    private readonly Action<string> _logger;

    public LoggingLocalizer(ILocalizer innerLocalizer, Action<string> logger)
    {
        _innerLocalizer = innerLocalizer;
        _logger = logger;
    }

    public string Localize(string enStr)
    {
        var result = _innerLocalizer.Localize(enStr);
        _logger($"Localize('{enStr}') -> '{result}'");
        return result;
    }

    public string LocalizeByKey(string key)
    {
        var result = _innerLocalizer.LocalizeByKey(key);
        _logger($"LocalizeByKey('{key}') -> '{result}'");
        return result;
    }
}

// Usage
var baseLocalizer = new RussianLocalizer();
LocalizedStrings.Localizer = new LoggingLocalizer(
    baseLocalizer,
    msg => Console.WriteLine($"[LOCALIZATION] {msg}")
);

Integration with .NET Attributes

The localization system integrates seamlessly with .NET's DisplayAttribute for declarative localization in data models:

Using with Enum Types

using System.ComponentModel.DataAnnotations;
using Ecng.Localization;

public enum LogLevels
{
    [Display(ResourceType = typeof(LocalizedStrings), Name = nameof(LocalizedStrings.InheritedKey))]
    Inherit,

    [Display(ResourceType = typeof(LocalizedStrings), Name = nameof(LocalizedStrings.VerboseKey))]
    Verbose,

    [Display(ResourceType = typeof(LocalizedStrings), Name = nameof(LocalizedStrings.DebugKey))]
    Debug,

    [Display(ResourceType = typeof(LocalizedStrings), Name = nameof(LocalizedStrings.InfoKey))]
    Info,

    [Display(ResourceType = typeof(LocalizedStrings), Name = nameof(LocalizedStrings.WarningsKey))]
    Warning,

    [Display(ResourceType = typeof(LocalizedStrings), Name = nameof(LocalizedStrings.ErrorsKey))]
    Error
}

// Usage with Ecng.ComponentModel extensions
using Ecng.ComponentModel;

var level = LogLevels.Warning;
string displayName = level.GetFieldDisplayName(); // Gets localized "Warnings"

Using with Class Properties

using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using Ecng.Localization;

public class LogSource
{
    [Display(
        ResourceType = typeof(LocalizedStrings),
        Name = nameof(LocalizedStrings.IdKey),
        Description = nameof(LocalizedStrings.IdKey),
        GroupName = nameof(LocalizedStrings.LoggingKey),
        Order = 1)]
    public Guid Id { get; set; }

    [Display(
        ResourceType = typeof(LocalizedStrings),
        Name = nameof(LocalizedStrings.NameKey),
        Description = nameof(LocalizedStrings.LogSourceNameKey),
        GroupName = nameof(LocalizedStrings.LoggingKey),
        Order = 2)]
    public string Name { get; set; }

    [Display(
        ResourceType = typeof(LocalizedStrings),
        Name = nameof(LocalizedStrings.LogLevelKey),
        Description = nameof(LocalizedStrings.LogLevelDescKey),
        GroupName = nameof(LocalizedStrings.LoggingKey),
        Order = 3)]
    public LogLevels LogLevel { get; set; }
}

Custom Resource Keys

Extend LocalizedStrings with your own resource keys:

using Ecng.Localization;

public static class MyLocalizedStrings
{
    // Define keys
    public const string UserNameKey = nameof(UserName);
    public const string PasswordKey = nameof(Password);
    public const string LoginButtonKey = nameof(LoginButton);

    // Define properties that use the localizer
    public static string UserName => UserNameKey.LocalizeByKey();
    public static string Password => PasswordKey.LocalizeByKey();
    public static string LoginButton => LoginButtonKey.LocalizeByKey();
}

// Usage in attributes
public class LoginModel
{
    [Display(
        ResourceType = typeof(MyLocalizedStrings),
        Name = nameof(MyLocalizedStrings.UserNameKey))]
    public string UserName { get; set; }

    [Display(
        ResourceType = typeof(MyLocalizedStrings),
        Name = nameof(MyLocalizedStrings.PasswordKey))]
    public string Password { get; set; }
}

Best Practices

1. Initialize Localizer Early

Set up your localizer during application startup:

public class Program
{
    public static void Main(string[] args)
    {
        // Initialize localization before anything else
        InitializeLocalization();

        var app = CreateApplication();
        app.Run();
    }

    private static void InitializeLocalization()
    {
        var culture = GetUserPreferredCulture();
        LocalizedStrings.Localizer = new MyLocalizer(culture);
    }
}

2. Use Resource Keys for Stability

Prefer LocalizeByKey() over Localize() for better refactoring support:

// Good: Key-based (won't break if English text changes)
public const string ErrorKey = "ERROR_INVALID_INPUT";
string message = ErrorKey.LocalizeByKey();

// Less ideal: Text-based (fragile to typos and changes)
string message = "Invalid input".Localize();

3. Provide Fallback Behavior

Always return meaningful fallback text:

public string Localize(string enStr)
{
    // Try translation
    if (_translations.TryGetValue(enStr, out var result))
        return result;

    // Fallback to original (better than throwing exception)
    return enStr;
}

4. Don't Set Localizer to Null

The library explicitly prevents null localizers:

// This will throw ArgumentNullException
LocalizedStrings.Localizer = null; // ERROR!

// Instead, use a pass-through localizer if needed
LocalizedStrings.Localizer = new PassThroughLocalizer();

5. Cache Translations When Possible

Avoid repeated lookups for frequently used strings:

// Cache in a field or property
private readonly string _errorMessage = LocalizedStrings.Errors;

public void LogError()
{
    // Reuse cached translation
    Console.WriteLine(_errorMessage);
}

6. Test Missing Translations

Implement tests to catch missing translations:

[Test]
public void AllKeysHaveTranslations()
{
    var localizer = new RussianLocalizer();
    LocalizedStrings.Localizer = localizer;

    // Test all predefined keys
    Assert.AreNotEqual("Name", LocalizedStrings.Name);
    Assert.AreNotEqual("Errors", LocalizedStrings.Errors);
    Assert.AreNotEqual("Warnings", LocalizedStrings.Warnings);
}

API Reference

ILocalizer Interface

public interface ILocalizer
{
    /// <summary>
    /// Localizes a string using the English text as the lookup key.
    /// </summary>
    /// <param name="enStr">The English string to localize.</param>
    /// <returns>The localized string, or the original if not found.</returns>
    string Localize(string enStr);

    /// <summary>
    /// Localizes a string using a resource key for lookup.
    /// </summary>
    /// <param name="key">The resource key.</param>
    /// <returns>The localized string, or the key if not found.</returns>
    string LocalizeByKey(string key);
}

LocalizedStrings Class

Properties

public static class LocalizedStrings
{
    /// <summary>
    /// Gets or sets the global localizer instance.
    /// Cannot be set to null.
    /// </summary>
    public static ILocalizer Localizer { get; set; }

    // Predefined localized string properties
    public static string Inherited { get; }
    public static string Verbose { get; }
    public static string Debug { get; }
    public static string Info { get; }
    public static string Warnings { get; }
    public static string Errors { get; }
    public static string Off { get; }
    public static string Id { get; }
    public static string Logging { get; }
    public static string Name { get; }
    public static string LogSourceName { get; }
    public static string LogLevel { get; }
    public static string LogLevelDesc { get; }
    // ... and more
}

Resource Keys

public static class LocalizedStrings
{
    // Resource key constants for use with DisplayAttribute
    public const string InheritedKey = "Inherited";
    public const string VerboseKey = "Verbose";
    public const string DebugKey = "Debug";
    public const string InfoKey = "Info";
    public const string WarningsKey = "Warnings";
    public const string ErrorsKey = "Errors";
    public const string OffKey = "Off";
    public const string IdKey = "Id";
    public const string LoggingKey = "Logging";
    public const string NameKey = "Name";
    // ... and more
}

Extension Methods

public static class LocalizedStrings
{
    /// <summary>
    /// Localizes a string using English text as the key.
    /// </summary>
    public static string Localize(this string enStr);

    /// <summary>
    /// Localizes a string using a resource key.
    /// </summary>
    public static string LocalizeByKey(this string key);
}

Usage Examples

// Get localized string via property
string name = LocalizedStrings.Name;

// Get localized string via extension method
string custom = "My Text".Localize();

// Get localized string via key
string byKey = "CustomKey".LocalizeByKey();

// Use in DisplayAttribute
[Display(ResourceType = typeof(LocalizedStrings), Name = LocalizedStrings.NameKey)]
public string UserName { get; set; }

License

This project is part of the Ecng framework. Please refer to the main repository for licensing information.

Contributing

Contributions are welcome! When adding new localization features:

1. Ensure backward compatibility
2. Add resource keys to LocalizedStrings class
3. Provide both key constants and localized properties
4. Update documentation with examples
5. Add unit tests for new functionality

Support

For issues, questions, or contributions, please refer to the main Ecng repository.