It is related to https://bugzilla.wikimedia.org/show_bug.cgi?id=48308 but I'm opening a new ticket instead of reopening the former one (people feel better if they work on new tickets).

According to https://uk.wikisource.org/w/api.php?action=query&meta=siteinfo&siprop=general|namespaces|namespacealiases the following things are needed to be fixed:

250:"Сторінка" should have "Page" as a canonical namespace.
251:"Обговорення сторінки" - "Page talk"
252:"Індекс" - "Index"
253:"Обговорення індексу" - "Index talk"
102:"Автор" - "Author" (instead of having it as an alias)
103:"Обговорення автора" - "Author talk" (again, instead of having it as an alias)

Version: wmf-deployment
Severity: enhancement
URL: https://uk.wikisource.org/w/api.php?action=query&meta=siteinfo&siprop=general|namespaces|namespacealiases