enable Hindi on native keyboard of iOS 5 by Sagarganatra

Step 1:
Open the settings; press on the 'General' option and then go to keyboard.

Step 2:
Scroll down a bit and select the "International Keyboard"

Step 3:
Select the 'Add New Keyboard' from the option

Step 4:
Scroll down and choose Hindi from the list of available keyboard languages. After that the selected language will be added to the list of enabled keyboards.

Step 5:

Whenever there is a need to enter Hindi text, press and hold the Globe icon on the keyboard to choose the Hindi language keyboard from the list.
To change the input language back to English, press and hold the Globe icon on the keyboard to choose the English from the list.