假设您有下面的类和这些对象的列表

public class Post
{
    public int PostId { get; set; }
    public string Language { get; set; }
    public string Name { get; set; }
    public string Value { get; set; }
}

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然后你可以编写以下LINQ查询：

var posts = new List<Post>
{
    new Post { PostId = 1, Language = "en", Name = "title", Value = "Post 1 title" },
    new Post { PostId = 1, Language = "en", Name = "body", Value = "This is the content for the post 1" },
    new Post { PostId = 1, Language = "fr", Name = "title", Value = "Titre de l'article 1" },
    new Post { PostId = 1, Language = "fr", Name = "body", Value = "Voici le contenu de l'article 1" },
    new Post { PostId = 2, Language = "en", Name = "title", Value = "Post 2 title" },
    new Post { PostId = 2, Language = "en", Name = "body", Value = "This is the content for the post 2" },
    new Post { PostId = 3, Language = "en", Name = "title", Value = "Post 3 title" },
    new Post { PostId = 3, Language = "en", Name = "body", Value = "This is the content for the post 3" },
    new Post { PostId = 3, Language = "fr", Name = "title", Value = "Titre de l'article 3" },
    new Post { PostId = 3, Language = "fr", Name = "body", Value = "Voici le contenu de l'article 3" },
    new Post { PostId = 3, Language = "de", Name = "title", Value = "Titel von Artikel 3" },
    new Post { PostId = 3, Language = "de", Name = "body", Value = "Lesen Sie den Inhalt von Artikel 3" }
};

var result = posts
    .GroupBy(x => 1)
    .ToDictionary(x => "posts",
        p => p.GroupBy(bp => bp.PostId)
            .ToDictionary(bp => bp.Key,
                bp => bp.GroupBy(lp => lp.Language)
                    .ToDictionary(lp => lp.Key, lp => lp.ToDictionary(n => n.Name, n => n.Value))
            )
    );

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我想你需要把这个DataTable转换成JSON。为此，您可以使用.NET中的Newtonsoft Json库并将数据序列化为有效的JSON。
大概是这样的：

string result;
result = JsonConvert.SerializeObject(dt); //where dt is content of DataTable

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更多信息Newtonsoft Json

为什么不创建一个表示该对象类呢？
下面是一个可以用于您示例的类：

internal class Post
{
    public int PostId { get; set; }
    public string Language { get; set; }
    public string Name { get; set; }
    public string Value { get; set; }
}

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要将SQL查询的结果转换为该类的示例，可以使用ORM。对于这个例子，你可能想使用一个微型ORM，比如dapper，他会看到这个链接https://www.learndapper.com/dapper-query/selecting-multiple-rows

using (var connection = new SqlConnection(connectionString))
{
    var sql = "SELECT * FROM yourTable"; // Careful: perf! You might want filters
    var posts = await connection.QueryAsync<Post>(sql);
    
    foreach(var post in posts)
    {
        Console.WriteLine($"{post.PostId} {post.Language} {post.Name} {post.Value}");
    }
}

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一些可以使用LINQ执行的查询示例：

var engPosts = posts.Where(x=>x.Language == "ENG").ToList();
var allTittles = posts.Where(x=>x.Name=="Title").ToList();

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请记住，根据您的用例，您可能希望在此数据结构之上使用其他数据结构，以提高性能，可用性，搜索等。

您可以创建一个对象模型，由包含不同语言内容的帖子组成。

public class Content
{
    public string Title { get; set; }
    public string Body { get; set; }
}

public class Post
{
    public int Id { get; set; }
    public Dictionary<string, Content> LocalizedContent { get; } = new();
}

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范例：

List<Post> posts = new();

var post = new Post { Id = 1 };
post.LocalizedContent["en"] = new Content { 
    Title = "Post 1 title", 
    Body = "This is the content for the post 1"
};
post.LocalizedContent["fr"] = new Content {
    Title = "Titre de l'article 1",
    Body = "Voici le contenu de l'article 1"
};
posts.Add(post);

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一个帖子包含一个内容字典，其中语言被用作关键词。这允许您向帖子添加不同的本地化内容。
在DB中，您将有两个表：

TABLE Post
    Id int PRIMARY KEY

TABLE Content
    PostId int PRIMARY KEY, FOREIGN KEY
    Language char(2) PRIMARY KEY
    Title varchar(80)
    Body varchar(max)

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语言也可以是包含支持的语言沿着完整语言名称的语言表中的外键。

对于喜欢C#严格代码的人

var result = new Dictionary<int, Dictionary<string, PostItem>>();
    
    var postsG = posts.GroupBy(p => new { p.PostId });
    foreach (var item in postsG)
    {
        var posGG = item.GroupBy(i => i.Language);
        var dict = new Dictionary<string, Item>();
        foreach (var p in posGG)
        {
            var i = new PostItem();
            foreach (var pp in p)
                if (pp.Name == "title") i.title = (string)pp.Value;
                else i.body = (string)pp.Value;
            dict.Add(p.Key, i);
        }
        result.Add(item.Key.PostId, dict);
    }

public class PostItem
{
    public string title { get; set; }
    public string body { get; set; }
}

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输出量

JsonConvert.SerializeObject(result, Newtonsoft.Json.Formatting.Indented);

{
  "1": {
    "en": {
      "title": "Post 1 title",
      "body": "This is the content for the post 1"
    },
    "fr": {
      "title": "Titre de l'article 1",
      "body": "Voici le contenu de l'article 1"
    }
  },
  "2": {
    "en": {
      "title": "Post 2 title",
      "body": "This is the content for the post 2"
    }
  },
  "3": {
    "en": {
      "title": "Post 3 title",
      "body": "This is the content for the post 3"
    },
    "fr": {
      "title": "Titre de l'article 3",
      "body": "Voici le contenu de l'article 3"
    },
    "de": {
      "title": "Titel von Artikel 3",
      "body": "Lesen Sie den Inhalt von Artikel 3"
    }
  }
}

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