From “Why I love MediaWiki” by Brianna Laugher:
My single favourite thing about it is the ability (for sysops at least) to edit the interface, via editing pages in the MediaWiki: namespace. It really steps back and lets the users take ownership of their wiki. It makes me wish practically all software I used had such a function. (Unfortunately the “discoverability” of this fact is still low. Your chances of figuring this out without anyone telling you would be near zero.)
Yes, in MediaWiki an administrator can change just about every piece of text that users see, just by editing the corresponding page. It’s a pretty ingenious approach to customization, though it’s true that it’s hard to find out: I actually had to re-learn that fact a few times before I really remembered it, because it’s such an unexpected feature.