How do I translate text I typed myself into banners and page sections?

Use a custom string. Open Plugins, then Multi Language, go to the Translations tab and click + Add custom string. Give it a key and the English value, then add the translations. Click the copy button next to the string to copy its token, and paste that token into your banner, heading or text block in the page builder instead of the plain text. Shoppers then see the version for their chosen language.