using System;

using AutoMapper;

public class Program

{

    public static void Main()

    {

        var lang = "tr";

        var sourceTest = new SourceItem();

        sourceTest.title = "test title";

        Mapper.CreateMap<SourceItem, TargetItem>()

            .ForMember(d => d.lang, opt => opt.ResolveUsing(res => res.Context.Options.Items["LangItem"]));

        var targetTest = new TargetItem();

        targetTest = Mapper.Map<SourceItem, TargetItem>(sourceTest, opt => opt.Items["LangItem"] = lang);

        Console.WriteLine("lang : " + targetTest.lang);

    }

    public class SourceItem

    {

        public string title{get;set;}

    }

        public class TargetItem

    {

        public string title{get;set;}

        public string lang{get;set;}

    }

}