Buttons in dialogs
should use text and that's what you see in almost all our dialogs. It's
also what Microsoft does in its dialogs (can't speak for Mac or Linux).
-1 for using emojis.
On Linux the GTK3 UX approach has been to remove stock icons from many places, including buttons. You will be hard pressed to find icons in buttons in up-to-date native GTK/GNOME apps. I'm not a fan of adding icons to dialog buttons, because on Linux (and Windows it seems) it will look out of place. In general I'd suggest removing as many buttons as possible, and replacing them with more intuitive solutions -- for example: inline editing vs. an "edit" button with a popup dialog. IMO this is far cleaner and provides a bigger UX benefit in the long run.