My iPod Touch is set to French, and Plants vs Zombies picked that up and presents the game in French. The translation is just awful. Is there a way to un-localize it so it's in English, is it locked like this, or did I download the wrong version?
The only way I know of is to set your iPod to English.
I just tested this. Even though the App Store only displays the localized (in my case german: 'Pflanzen gegen Zombies') version to me, the game itself is in English as long as the system language is set to English.
After you changed your system language, the game's language should've changed as well. There is no need to redownload/reinstall the game.