> What if traffic signs had text for many years and then suddenly a bunch were replaced by new ones with only a new icon and no visible explanation of what the icon means?

That's... exactly how meaningful icons are born. First you put icon with text, and once everyone understands the meaning of the icon, you remove the text, because it's not necessary anymore.

Do you think that US drivers would be left completely clueless when seeing the "yield" sign without the text, or would they recognize the icon?

> Not even close to the situation with mystery UIs in computer programs.

Android UI offers three buttons at the bottom of the screen. There's never been any text there. Yet somehow, most people have no issues using them. How come? Follow-up question: if you wanted to put text there, whete exactly would you do that, and what would it say? In real life, what about public toilets? Many places don't have a text "toilet", they just have a symbol of two stick figures, one wearing a skirt, yet we're all fine. Emergency exit? Sometimes it's without text, just a green light with a white stickman running through a door. Red X is also widely recognized as "closed" or "don't enter".

Finally, please tell me what you see in top-right corner of a window in your computer. If you see spelled out words "minimize", "maximize", "close" then yeah. Otherwise I'd like to ask you what makes these three buttons so special that they don't need text.

Payment terminals have green-yellow-red buttons at the bottom. No text, just icons and colors.

Point is, "icon without text" is an idea that exists in the wild and works.