Here's how you can change the dialect in Speak Selection on your iPad, iPhone or iPod.
1. Go to Settings.
2. Go to General.
3. Tap on Accessibility. Tap on Speak Selection.
4. Tap on Dialects.
5. Tap on your preferred dialect from the list of options:
English Espanol French Nederlands Portugese Other Languages
For more, see the original article at the link below.