public class CustomRepository : InProcItemModelRepository
  {
    public override Guid Create(string itemName, Guid templateId, Guid parentId, string language)
    {
      var parentItem = base.Get(parentId);
      if (parentItem == null)
      {
        return Guid.Empty;
      }
      var path = parentItem[ItemModel.ItemPath].ToString();
      //
      var itemModel = new ItemModel();
      itemModel[ItemModel.ItemName] = itemName;
      itemModel[ItemModel.TemplateID] = templateId.ToString();
      var handler = base.HandlerProvider.GetHandler<CreateItemHandler>();
      var command = new CreateItemCommand
      {
        ItemModel = itemModel,
        Path = path,
        Language = language

      };
      var response = handler.Handle(command) as CreateItemResponse;
      return response.ItemId;
    }

    public override bool Update(Guid id, ItemModel itemModel, string language, int version)
    {
      var handler = base.HandlerProvider.GetHandler<UpdateItemHandler>();
      var command = new UpdateItemCommand
      {
        Id = id,
        Database = base.DatabaseName,
        ItemModel = itemModel,
        Language = language,
        Version = version.ToString()
      };
      handler.Handle(command);
      return true;
    }
  }

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
    <sitecore>
        <dataExchange>
            <itemModelRepository type="Custom.DataExchange.CustomRepository, Custom.DataExchange", patch:instead="processor[@type='Sitecore.DataExchange.Local.Repositories.InProcItemModelRepository, Sitecore.DataExchange.Local']">
                <databaseName>master</databaseName>
            </itemModelRepository>
        </dataExchange>
    </sitecore>
</configuration>

var repo = (CustomRepository)DataExchange.Context.ItemModelRepository;
var templateId = new Guid("{A0691A54-6175-4C10-9E10-9A1FA0134517}");
var parentId = new Guid("{110D559F-DEA5-42EA-9C1C-8A5DF7E70EF9}");
var itemId = repo.Create("My Product", templateId, parentId, "de");
repo.Update(itemId, new ItemModel() { { "ProductName", "My Product Name" } }, "de", 1);