By default, voice reminder messages are set to English American.
You have the following language options when sending voice messages:
English with an American accent
English with a British accent
Login to Appointment Reminder and go to Scripts > Edit Scripts and click edit on the script you wish to edit.
Click on "Voice" in the left menu.
You will see an option down the page that says "Language".
Change this to the language you wish to use and click Save on left.