If it is json encoded, you can use the same approach in c# also. Use a json deserializer.
Depending on what you want to do with it, a simple method is using FastJson
] for example:
var newobj = fastJSON.JSON.Instance.Parse(@"[[2, 3], [3, 4], [5, 6]]");
You will get a List<list<object>> where every element will be an Int64. I am not sure, that converting this to array is really necessary.