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.

The popular reason is likely because 文 is used across East Asia in Chinese and Japanese (Korean and Vietnamese too, though written differently)[0], with the ideograph standing in as a sufficiently different contrast to the Latin alphabet, and as a reference to a major non-latin-alphabet based user market, while being simple enough to render (compared to something more "difficult"[1] like 语/語)

It's also been used in the Google Translate logo as well.

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[0] https://en.wiktionary.org/wiki/%E6%96%87

[1] Not only because of Simplified/Traditional/Japanese renderings (文 is mostly the same across all three), but more strokes for a small icon is a bad idea regardless

It’s a Chinese character and a Latin letter. The idea, presumably, being that of ‘multiple languages’.

But I don’t know Chinese so I don’t know that is an arbitrary Chinese character with the Latin A for contrast. I’ve seen languages that don’t use the Latin alphabet occasionally intersperse Latin letters before so until I was told just now I assumed that this Chinese character with A had some significance in Chinese.

So I don’t think it’s very effective at that.

Really? When I first saw it I understood it must have to do with changing languages.

Never struck me that way, though I can see it in retrospect. On the other hand, if I see a flag, I know that’s language settings.

In don’t know that using flags for language settings is more semantic, but it’s convention so I know what it means.

I’ve seen flags used to indicate language settings for as long as I’ve been using computers.

Visiting the Netherlands right now and every time I visit local.google.com, it reverts back to Dutch. I had no idea what the symbol on its own and only figured it out when searching how to get things back to English and seeing the symbol used in that specific context.

I thought it was a weird logo or something, no idea it was even a button.

I recall thinking it was a compass before. They should've chosen a more complicated Chinese character if that is what they wanted to portray.