Here is how I enable Vietnamese writing on my iPhone 4. It might work on the iPod touch and iPad as well.
Enable the Vietnamese Keyboard
- Pre IOS 7: On the iPhone, go to Settings, General, Keyboard, International Keyboards, and Add new Keyboard…
- IOS 7: Settings > General > Keyboard > Keyboards > Add New Keyboard
- Select the Vietnamese keyboard from the list and add
- Exit out of the Settings
On the soft keyboard, a new button appears to the left of the spacebar and it has the picture of the globe. This button switches the keyboard from English to Vietnamese and back. Once switched to Vietnamese, the following key combinations are available:
- aa – â
- aw – ă
- ee – ê
- oo – ô
- ow – ơ
- uw – ư
- dd – đ
- as – á
- af – à
- ar – ả
- ax – ã
- aj – ạ
Thank you Mr. Chien Nguyen for his wonderful tip. I found I use it more than my own tip.
You can also hold down a vowel, then iPhone 4 (maybe other iPhones as well) will prompt you a set of characters with accents for that vowel. You then just select the one that you want.