While Plone developers and those upgrading from past plone themes may understand the meaning behind some/ most/ all of the icons, new users to Pastanaga may not understand what action will be performed from clicking/ tapping an icon. Adding some text labels beneath the icons would make Pastanaga more understandable and approachable.
I think the aim is like in the main mobile os, that icons doesn't needing explanation. the user should easily understood the action behind. if pastanaga reached the goal, i don't know.
Any image (icon) without a textual description (alt text, aria-label, ...) is a violation of accessibility guidelines.
FYI: We added alt tags and aria labels in Volto 4. They should be there.