It's just determining someone's gender based on name, how hard could it be?

Determining someone's gender based on name won't be a difficult task if you know the name pattern. This task can be difficult to accomplish when you're not familiar with the name pattern. Since I'm Indonesian heavily influenced with American and Muslims influence. Indonesian names or British or American or Islamic names would be familiar for me. So I can determine the gender easily. But when it comes determining chinese or thai or vietnamese name I found it quite difficult.
I just made two mistake. First mistake I thought a thai girl as a guy and second mistake I did the same thing to pakistani girl. Thank God they're not angry. Well at least the thai girl didn't. The pakistani girl didn't know yet because I haven't made any contact yet. Thanks to shailendra for telling her gender. I think because India and Pakistan have the same root made him knows the pakistani name pattern just like indonesia and malaysia.
Since Indonesia has hundreds of tribes and almost each tribe has their own language and could be they have their own name pattern. The same bias could exist even when you have to determine gender based on other tribe's name pattern. For example Endang in Javanese is considered as a female name but in Sundanese is considered as a male name with a different pronunciation. I had experienced this difficulty when I have to write a letter for a person named Endang. Since I'm in bandung which is the capitol city for Sundanese I can't determine what title I should wrote Mr. or Mrs. Although Bandung is capitol city for Sundanese there're lots of Javanese here. I'm a Javanese too and living here in Bandung.
Next time I have to be careful in determining someone's gender based on name especially if I don't familiar with the name pattern.