Translation using Google Api - iphone

Question

this is the code i am using to translate from English to Vietnamese.
NSString *urlPath = [NSString stringWithFormat:#"/translate_a/t?client=t&text=%#&langpair=en|vi",txt_view.text];
NSURL *url = [[NSURL alloc] initWithScheme:#"http"
host:#"translate.google.com"
path:urlPath];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:url];
[request setHTTPMethod:#"GET"];
NSURLResponse *response;
NSError *error;
NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
if(error == nil)
{
NSString *result = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
NSLog(#"Result : %#", result);
NSArray *arr = [api tocanizeTheString:result tocan:#","];
result = [arr objectAtIndex:0];
result = [api replaceStringwithString:result strTobeReplaced:#"[" stringReplaceWith:#""];
result = [api replaceStringwithString:result strTobeReplaced:#"\"" stringReplaceWith:#""];
txt_view.text = result; // here i get only translated data...
}
else
{
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
some times it give accurate result and sometimes it doesn't. please tell me whats the problem.
"My name is Taimur Mushtaq" i type this in my app, it shows correct result which is "Tên tôi là Taimur Mushtaq".
"I am a good boy" the result should be "Tôi là một chàng trai tốt". instead it is "tôi là m\u1ED9t c\u1EADu bé t\u1ED1t"