How to use Roboto and San Francisco fonts in the same app on both Android and iOS platforms?

Question

Design

There is an application for iOS and Android, they use the Arial font, which they want to replace with another one. Question: Is it correct to use San Francisco for iOS and Roboto for Android, or is it better to choose the same font for both platforms? And what about system elements, for example, pop-ups that will use the system font. And it will be strange if the application uses Arial, for example, and popups and all other system stuff will be with the system font.
Are there rules on how to properly use fonts for different platforms? And from an aesthetic point of view. we can't just use system fonts all the time, can we? How will other fonts be combined with system fonts in one application?

Answer 1

It is normal and good practice to use native fonts for each platform. And by default, you should stick to it.
Using your own font is also normal practice. But usually it only makes sense if the company has a good, clear corporate identity, brand book, and that's it. Most often they are, if you are some kind of Beeline or Volkswagen. If you are a small desk and especially indie developers - most likely you don’t need it (if you had clear reasons for using your font, you wouldn’t ask this question here, but would decide with your in-house designer).