/static/images was created in 145f5cea9f324137512101eb6f42458c91bfe40c as copy of /images/, and the latter was left behind as stale copy (not a symlink).
Some of the files in there are now out of sync. For example, wikipedia-wordmark-en.png has a registered trademark icon in /static/images/mobile/ the version in /images/mobile does not.
They also don't benefit from the cache rules set up for /static.
https://en.m.wikipedia.org/static/images/mobile/wikipedia-wordmark-en.png
https://en.m.wikipedia.org/images/mobile/wikipedia-wordmark-en.png