TranslationBinding.cs

internal sealed class TranslationBinding : IBinding
{
    private readonly IBinding _binding;

    public TranslationBinding(IBinding binding)
    {
        _binding = binding;
    }

    public InstancedBinding Initiate(IAvaloniaObject target, AvaloniaProperty targetProperty, object anchor = null, bool enableDataValidation = false)
    {
        var instance = _binding.Initiate(target, null);

        IBinding CreateTranslationBinding(string translationKey) =>
            new Binding($"[{translationKey}]")
            {
                Mode = BindingMode.OneWay,
                Source = TranslationManager.Instance,
            };

        var observable = from x in instance.Subject
                         from y in IsTranslation((string)x, out var key)
                            ? CreateTranslationBinding(key).Initiate(target, null).Subject
                            : Observable.Return(x)
                         select y;

        return new InstancedBinding(Subject.Create<object>(Observer.Create<object>(x => { }), observable), BindingMode.OneWay, instance.Priority);
    }
}