As a german, I feel the right side is much more alien to me than the left side (split at "Start here").

Is that circumstancial, or does it reflect some linguistic truth? Like, are the languages on the left one family, and the ones on the right another family, or however linguistic taxonomy would call that?

Maybe it's just that the left side includes all the germanic languages, so that feels more familiar. There are also languages on the left side where I have no clue what or where that might be. But much more so on the right side.

Swiss German doesn't have orthography and üü can absolutely appear.

Edit: They meant Schriftsprache/Schriftdeutsch, which is almost German but without the ß.

https://www.flagsarenotlanguages.com/blog/why-flags-do-not-represent-language/

The swedish one is incorrect. It's ä and ö not æ and ø.

The only source I found for the "kiillt saam" is this page. Was it meant to be Kildin Sámi?

I'm not sure what the c with a line on it is but Estonian (või siis Eesti keel) doesnt have it.

In primarily Irish speaking places you might find TH missing from the orthography entirely.

Similarly, I wonder if ä could show up in English. Such as in diäeresis.

I just use my innate knowledge of my fellow Europeans to identify the language well enough to point in the general direction which it came from, or maybe using cardinal directions like "south" or "east"