The currency used by the app when displaying prices is driven by your regional formats (check your General Settings on iPad). It is unrelated to the language. You can have an app in English showing prices in R$.
Here is how the price is displayed:
1. the app connects to the AppStore. Which Store ? This is the last store that you used on your iPad, or the store associated with your sandbox user if you used that user.
2. The app retrieves the price, given by the Store. For example, if you are connected to the US Store, and your in-app is worth 1,99$, it will return 1.99$
3. Then the regional settings are used to display the price. This means that a currency is added to your price. If your regional settings specify Portuguese > Brazil, the the displayed price will be R$ 1.99
Note in that case that no currency conversion is happening. It is impossible to do as Apple does not return converted prices, but only prices for the local store.
When you click on the purchase button, then Apple will take offer and print a confirmation message with the price expressed in the Store currency ($1.99 in that case)