I guess this poses the question: Is there a clear boundary between text and icons? And in which cases should icons be handled like characters?
Plain symbols within text clearly belong in a font. Logos, on the other hand, are images, not characters. Icon fonts, which are somewhere in between, became popular for webdesign but seem to be falling out of favor again. What is the current "best practice" here?
No, there is no clear boundary between text and icons. What is included in Unicode and in what way is decided case by case. See for example the regional indicator symbols.[1] Always two of them indicate a particular country code according to ISO 3166-1.[2] They resolve into a sort of a logo: the flag of the country. (Guess what happens with rendering a legacy Unicode document, when a country changes its flag ...)
I'll just add a meta comment that `understood (or not) irregardless` is the most value-ambiguous utterance I've read in a long while; quite clear to me what you meant, but probably would be quite a 'head scratcher' for an AI.
There is no entity that can decree something an international language or otherwise, even if an entity were arrogant enough to claim that it could do so.
Many writing systems evolved from what we might consider icons. The letter A comes from the head of an ox, which becomes much more obvious if you put it upside down like ∀. Many Chinese characters retain a similarity to the objects they represent: "tree" is 木 and "fire" is 火 (imagine a bonfire). The Korean consonants ㄱ and ㄴ represent the general position and shape of your tongue when you make the "k" and "n" sounds, respectively. All of these symbols began their life as icons, but were later recognized as text as people converged on a certain usage.
Plain symbols within text clearly belong in a font. Logos, on the other hand, are images, not characters. Icon fonts, which are somewhere in between, became popular for webdesign but seem to be falling out of favor again. What is the current "best practice" here?