Conjugations ES uses the speech engine and voices built in to every iOS device so that you can choose what kind of Spanish accent to listen to. You can currently choose to hear European Spanish pronunciation or Latin American Spanish pronunciation. If Apple makes more Spanish voices available in the future, we'll support those too.
We decide which voice to use for the Spanish speech in Conjugations ES by looking at the system preference for languages on your device. We'll use whichever Spanish language is higher in the list and has a matching voice.
You can find the list of languages supported by your device in Settings > General > Language. You can also change the order of the languages here.
If Español is higher than Español (México) in this list, you'll hear European Spanish pronunciation in Conjugations ES.
If Español (México) is higher than Español in this list, you'll hear Latin American Spanish pronunciation in Conjugations ES.