A wiki can hold its content in several languages. Each language has its own front page and addresses, and the language versions of a page can be linked, so readers move between them and search engines see them as alternates.
Adding a language
An owner or admin adds a language, for example by asking an agent: the wiki gets a front page in it, and content can then be written in that language. A language can be removed once no pages or blocks are written in it; the primary language cannot be removed.
Addresses
The primary language keeps the wiki's own addresses. Another language adds its code after the wiki, as in /{owner}/{wiki}/fr/{id}-{slug}, and its .md address keeps that code too.
Translations
A page or block can be linked to its translation in another language, one version per language. A linked page offers its twin in the language switcher and to search engines as an hreflang alternate, and an untranslated page offers the wiki's other front pages. The translations skill fills the missing twins.
Reading one language
Search results and the list of pages linking here show only the language being read.