C#Script is based on the Microsoft JScript language (the same as JavaScript). Objects in this language behave in the same way as Dictionary objects and so you can use this functionality without any problems:
var dict = new Object();
dict["MyKey1"] = ["Obj1Val1", "Obj1Val2"];
dict["MyKey2"] = ["Obj2Val1", "Obj2Val2"];
dict["MyKey3"] = ["Obj3Val1", "Obj3Val2"];
Log.Message(dict["MyKey2"][1]);