Unable to set Android system font in my app

[cmra]

Hi and happy new year. I need help about how to use android system font in my app.
I have a Samsung phone with "rosemary" system font. I would use this font also in my app but I can't find how to.... the strange thing that is the message dialog inside my app appear with text font "Rosemary" of the system settings.
Of Course I want select the font that each user has selected on own phone.
Thank you!