There are at least 5 Chinese wikis that still have logo variant overrides in site css (T273578), the current approach available in the config is to copy and paste the same logo definition 4 times.
They don't have a wordmark or tagline now, but they may have in the future, which will be a big duplication in the config.
As a part of the user interface, it should be able to follow the fallback chain defined as language properties, like the fallback for interface messages.
We also want to limit the fallback depth, since the fallback chain is not limited to the same group of variants, so I'd like to introduce a new key fallback.
'wmgSiteLogoVariants' => [ 'zhwiki' => [ 'zh-hans' => [ 'fallback' => [ 'zh-cn', 'zh-my', 'zh-sg' ], '1x' => '/static/images/project-logos/zhwiki-hans.png', '1.5x' => '/static/images/project-logos/zhwiki-hans-1.5x.png', '2x' => '/static/images/project-logos/zhwiki-hans-2x.png', 'wordmark' => [ 'src' => '/static/images/mobile/copyright/wikipedia-wordmark-zh-hans.svg', 'width' => 105, 'height' => 23, ], 'tagline' => [ 'src' => '/static/images/mobile/copyright/wikipedia-tagline-zh-hans.svg', 'width' => 103, 'height' => 15, ], ], ], ],