See e.g. this thread. Is it intentional that Flow displays interwiki links like external links?
Topic on Talk:Structured Discussions
Interwiki links display like external links
Interwiki links display like external links in Flow. This is not a conscious design feature but is not considered a major blocker either, because interwiki links are an intermediate category between internal links and external links. phab:T97552 tracks this design issue.
As the nice IP has summarized the topic, it is tracked as T97552. It is not intentional, and while it is not a major blocker (basically because it is an external link to another wiki), it hasn't been fixed.
Flow has been abandoned after it became clear it was a failure. Sorry.
News circulated at Wikimania 2017 that Flow is back in active development...!
(general discussion on the future of threaded discussions continue on this thread)