[derefr]

Wikipedia's UI has perhaps been over-optimized over time, by people already too familiar with said UI, and so has lost the natural context cues for learnability. (Similar to what happened to modern smartphone UIs re: secondary-interaction gestures.)

Here's how the same chooser looks on Wiktionary — which is also how it used to look on Wikipedia, back when Wikipedia used the full default MediaWiki sidebar: https://oshi.at/HhVH/zhWZ.png

You've got a subsection header "In other languages"; and under it, a list of links titled with the names of languages. (This reads as: these are a set of popular suggested alternative language views of this page, and clicking these links will take you directly to the page in those languages.) And at the end of this list, aligned as the final list item, there's a button with a weird icon with the text "51 more" on it. (And this reads as: clicking here will expand some flyout menu or modal, which will allow you to see you the rest of the list of language options, and perhaps search within them.)

In that context, you don't really have to understand the meaning of the icon to know what to do; rather, the interaction of changing language is directed by the rest of the design, and going through it teaches you the meaning of the icon. Which allows you to later understand its use elsewhere in the site's design.