Here's an excerpt from the ipod 5th gen. manual:
(Note that you won't see the names they give here in brackets, because they'll be in the wrong language. They give you the place where each of the functions are, to get you to the change the language function.)
" If you accidentally set iPod nano to use a language you don’t understand
You can reset the language:
Press and hold Menu until the main menu appears.
Use the Click Wheel to find the menu item that causes the iPod nano device name to
appear in the preview panel, and then choose it. That’s the Settings menu.
Choose the last menu item (Reset Settings).
Choose the first item (Reset) and select a language. "