I created a doccarchive that supports objc and swift using xcode build setting DOCC_EXTRACT_SWIFT_INFO_FOR_OBJC_SYMBOLS. When I made a docc document, I can select objc or swift on Xcode documentation like the yellow box of the below image.
However, when I rendered to a web server, that selection link is gone.
Blue box of the 2nd image works different way with yellow box of 1st image. The yellow one shows all functions. Even functions not written in that language are converted to other languages and displayed. But the blue one shows functions only written in the selected language.
Rendering follows.. https://developer.apple.com/documentation/xcode/distributing-documentation-to-other-developers#Host-a-documentation-archive-on-your-website