无法跟踪实体类型的实体框架实例

我有以下Entity Framework Core 1.1的实体和上下文：

public class Language {
  public String LanguageCode { get; set; }
  public virtual ICollection<LanguageI18N> LanguagesI18N { get; set; } = new List<LanguageI18N>();
}

public class LanguageI18N {
  public String LanguageCode { get; set; }
  public String TranslationCode { get; set; }
  public String Name { get; set; }        
  public virtual Language Language { get; set; }
}

public class Context : DbContext {

  public DbSet<Language> Languages { get; set; }
  public DbSet<LanguageI18N> LanguagesI18N { get; set; }

  public Context(DbContextOptions options) : base(options) { }

  protected override void OnModelCreating(ModelBuilder builder) {

    base.OnModelCreating(builder);

    builder.Entity<Language>(b => {
      b.ToTable("Languages");
      b.HasKey(x => x.LanguageCode);
      b.Property(x => x.LanguageCode).IsRequired(true).HasMaxLength(2).ValueGeneratedNever();        
    });

    builder.Entity<LanguageI18N>(b => {
      b.ToTable("LanguagesI18N");
      b.HasKey(x => new { x.LanguageCode, x.TranslationCode });      
      b.Property(x => x.LanguageCode).HasMaxLength(2).IsRequired(true);
      b.Property(x => x.TranslationCode).HasMaxLength(2).IsRequired(true);
      b.HasOne(x => x.Language).WithMany(x => x.LanguagesI18N).HasForeignKey(x => x.LanguageCode).IsRequired(true).OnDelete(DeleteBehavior.Restrict);
      b.HasOne(x => x.Language).WithMany(x => x.LanguagesI18N).HasForeignKey(x => x.TranslationCode).IsRequired(true).OnDelete(DeleteBehavior.Restrict);      
    });      

  }

}

然后我创建了一个语言，其翻译名称如下：

public class Program {

  public static void Main(String[] args) {

    DbContextOptionsBuilder builder = new DbContextOptionsBuilder<Context>();

    builder.UseInMemoryDatabase();

    using (Context context = new Context(builder.Options)) {

      Language language = new Language { LanguageCode = "en" };

      language.LanguagesI18N.Add(new LanguageI18N { LanguageCode = "en", TranslationCode = "en", Name = "English" });
      language.LanguagesI18N.Add(new LanguageI18N { LanguageCode = "en", TranslationCode = "pt", Name = "Inglês" });

      context.Languages.Add(language);

      context.SaveChanges();

    }         

  }

}

我正在使用代码“en”创建一种语言，并使用英语和葡萄牙语翻译其名称 .

当我运行代码时，我收到以下错误：

未处理的异常：System.InvalidOperationException：无法跟踪实体类型“LanguageI18N”的实例，因为已经跟踪了具有相同键的此类型的另一个实例 . 添加新实体时，对于大多数密钥类型，如果未设置密钥，则将创建唯一的临时密钥值（即，如果为密钥属性指定了其类型的默认值） . 如果要为新实体显式设置键值，请确保它们不会与现有实体或为其他新实体生成的临时值发生冲突 . 附加现有实体时，请确保只有一个具有给定键值的实体实例附加到上下文 .

我错过了什么？

UPDATE

该代码适用于InMemoryDatabase以及Ivan Stoev建议的更改：

b.HasOne<Language>().WithMany().HasForeignKey(x => x.TranslationCode).IsRequired(true).OnDelete(DeleteBehavior.Restrict);

但是当我替换InMemoryDatabase时：

builder.UseInMemoryDatabase();

通过SQL Server数据库：

builder.UseSqlServer(yourConnectionString);

我收到以下错误：

Unhandled Exception: Microsoft.EntityFrameworkCore.DbUpdateException: 
An error occurred while updating the entries. See the inner exception for details. ---> System.Data.SqlClient.SqlException: 
The INSERT statement conflicted with the FOREIGN KEY constraint "FK_LanguagesI18N_Languages_TranslationCode". 
The conflict occurred in database "TestDb", table "dbo.Languages", column 'LanguageCode'.
The statement has been terminated.

知道为什么吗？