Try looking at a wikipedia page on your phone. You could replace the 文A button with one that said "antidisestablishmentarianism" and there would still be plenty of space. It's floating at the left of an empty row.
I agree that the UX could be improved and there is plenty of evidence to support that. On the other hand the edit icon is super discoverable and used without the label so I think the challenge with the language icon is 1) there are not many multilingual sites and 2) the other icons there potentially cause the user to ignore them entirely.
Throw in the 200+ languages and longer labels in some of them and it becomes even more complicated...
Multilingual sites aren't rare at all. There is a conventional way to display a language selector: it's a button (usually a dropdown menu, if you click on it) with a national flag and the name of the language.
The big problem on mobile wikipedia is that wikipedia already has a well-established way to select the language you want to see the article in, and the mobile site completely removes it.
As I've said before the mobile site doesn't remove it. It just changes the mechanism for understandable reasons based on the medium.
Nice to chat to you.