You can create your own fonts with Fonty — the easy-to-use font making app that provides limitless font customization. From here you can export your fonts to other devices or applications including PicsArt.
You can download Fonty here.
You can also install open source fonts in .ttf format and use them on PicsArt. You just need to download the fonts to your device and move them to File Manager/PicsArt/Fonts. Make sure to check the license for the fonts you are going to download in order to avoid copyright issues. When you open the app and add text to your photo, you’ll find your custom fonts under the “My Fonts” tab.
This option is available only for Android devices for now.