In absence of Microsoft.Extensions.Localization and Microsoft.Extensions.DependencyInjection on .NET Framework < 4.6.1 (4.0, 4.5, 4.6) this class provides an easy access to localized resources

StringLocalizer.cs

/// <summary>
/// In absence of <see cref="T:Microsoft.Extensions.Localization"/> and <see cref="T:Microsoft.Extensions.DependencyInjection"/>
/// on .NET Framework &lt; 4.6.1 this class provides an easy access to localized resources
/// </summary>
/// <seealso cref="IDisposable" />
/// <inheritdoc />
public class StringLocalizer : IDisposable
{
    protected ResourceManager resourceManager;

    /// <summary>
    /// Initializes a new instance of the <see cref="StringLocalizer" /> class.
    /// </summary>
    /// <param name="assembly">The assembly containing localized string resources.</param>
    /// <param name="resourceLocation">The resource location, defaults to 'Properties.Resources'.</param>
    public StringLocalizer(Assembly assembly = null, string resourceLocation = "Properties.Resources")
    {
        var callingAssembly = assembly ??
                              new StackTrace().GetFrame(1).GetMethod()?.ReflectedType?.Assembly ?? 
                              Assembly.GetEntryAssembly();
        var rootNameSpace = callingAssembly.ManifestModule.GetTypes().Min(t => t.Namespace);
        resourceManager = new ResourceManager($"{rootNameSpace}.{resourceLocation}", callingAssembly);
    }

    /// <summary>
    /// Finalizes an instance of the <see cref="StringLocalizer" /> class.
    /// </summary>
    ~StringLocalizer()
    {
        ReleaseUnmanagedResources();
    }

    /// <summary>
    /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
    /// </summary>
    /// <inheritdoc />
    public void Dispose()
    {
        ReleaseUnmanagedResources();
        GC.SuppressFinalize(this);
    }

    /// <summary>
    /// Releases the unmanaged resources.
    /// </summary>
    private void ReleaseUnmanagedResources()
    {
        resourceManager?.ReleaseAllResources();
    }

    /// <summary>
    /// Gets the <see cref="System.String"/> with the specified string.
    /// </summary>
    /// <value>
    /// The <see cref="System.String"/>.
    /// </value>
    /// <param name="str">The string.</param>
    /// <returns></returns>
    public string this[string str]
    {
        get
        {
            try
            {
                return resourceManager.GetString(str);
            }
            catch
            {
                return str;
            }
        }
    }
}