On commons, I'm getting default sidebar, instead of customized version from [[commons:MediaWiki:Sidebar]]. My user language is english. This happens to me both when logged in and logged out.
(If this happens on non-en wikis, it would probably be pretty serious).
Relevant thread: https://commons.wikimedia.org/wiki/Commons:Village_pump#Where.27s_the_upload_button.3F
Version: unspecified
Severity: major
Confirmed works for me now (I'm on a different computer now)
I think we should still keep this open. The issue suggests something bad happening in i18n cache. We should probably try and see if we can figure out what happened and if it would happen again.
I believe this is a known thing existing for years: when message cache (for MediaWiki namespace) creation takes too long (usually when all caches are empty), MediaWiki will skip it and display the default messages, which will then get cached in the separate sidebar cache.