The Google APIs should support any of the translations that the online functionality does. In this case this would be Chinese "simplified" and "traditional" versions.
However, if you want to type in Chinese characters into an input box you would have to design some form of key-mapping that would allow such characters to be typed into the text-box, if you haven't already applied such capability. Once entered, then you can take the string of characters and send them to the APIs as the example demonstrates for Russian...
public class QuickStart
public static void Main(string args)
Console.OutputEncoding = System.Text.Encoding.Unicode;
TranslationClient client = TranslationClient.Create();
var response = client.TranslateText("Hello World.", "ru");