To translate the Pagefly app's resources, go to Translations -> Pagefly. Once there, click the Sync button:
The Synchronization process will gather all the resources coming from the Pagefly builder and allow you to translate them. Once it's complete, you can either translate all the resources manually or with AI, by clicking the Bulk translate button:
Make sure you have the "Custom translations" app embed enabled in your theme Customizer -> App embeds so that the Pagefly translations are active on your store.
In case you add additional resources/pages through the Pagefly builder, or, you modify any existing content, you need to Sync the resources again, then translate the new content. This is necessary since Pagefly does not support the multi-language feature and does not store its resources on Shopify's servers as "translatable" resources.