localization keyboard ?

Are you sure that there's no built-in Vietnamese keyboard when the device's locale is set to Vietnamese?

First, you might want to use up one of your DTS incidents on this and get Apple's help. They might be able to give you a lot of example code.

Barring that, conceptually a keyboard is straightforward but there are a lot of details to get right if you want to make one like Apple's keyboards. You need your own SearchBar class based on UITextField. This class shows the keyboard. The keyboard is probably an image with all the buttons on it. Your touch handling code will know the rectangles for all the 'buttons' and will enter a character into the text field when the user taps. Things like the spelling helper window or the magnifying glass or copy paste make this a large task however.