Configure iPad 2 interface languages? How can I configure my iPad 2 interface languages, to allow using English as system language and, when writing, be able to have Spanish word recognition auto-complete?
In the latest public release of iOS, you need to follow these steps: 


Tap on the Settings icon. 
Tap on General.
Tap on International. 
Tap on Keyboards. 
Tap on Add New Keyboard. 
Select Spanish. 


The Spanish keyboard is now added system-wide in addition to your default keyboard (let's say it was English for this example). Now whenever you see a keyboard layout on your screen, you will see a new button with a globe icon on it on the bottom-left corner of the screen, right next to the "123" button that switches to the numeric/symbolic keyboard. 

The globe button works like the "123" button in that it alternates between your International keyboard layouts. In this example, it will alternate between English and Spanish layouts. The spell checking and the auto-complete only work for whichever language you have have selected. In other words, you won't get English auto-complete when the layout is Spanish, which makes sense.

I use this feature all the time when composing e-mail messages in Spanish. Here's another tip: Tap and hold on the "n" key to get access to the "ñ" character. Also, tap and hold on any vowel to get the "á", "é", "í", "ó", "ú" and "ü" characters. 

Hope this helps.