Last modified: 2012-04-16 09:15:54 UTC
The appearance is that sidebar shows some default links but not those defined in MediaWiki:Sidebar on zhwiki (note that there're maybe complex fallback chain in zh language). This issue has been talked about some time ago in IRC but I cannot find the discussion now.
When I compare "Mediawiki:Sidebar" with the sidebar on zhwiki I don't see any difference.
I would say it's unstable. Sometimes this problem appears (not very often) and disappears soon.
This problem appears from time to time. Purging MediaWiki:sidebar page fixes it.
I don't know if my further comment is relevant to the issue, but it looks like it is. In be-x-old.wikipedia.org ($wgLanguageCode = 'be-tarask'), if I set my UI language 'be-x-old', then overriden messages in MediaWiki spacename are not used. If I set UI language back to 'be-tarask', then it's OK. I think a language mapping check should be performed. If the active language is mapped to another one and that language is the base language ($wgLanguageCode), then it should use MediaWiki: overrides, not the default messages.
I'm pretty sure this is a duplicate of a bug number around or below 10k