As of June 05 2019 interwiki linking for non-en-wikis of non-Wikipedias (e.g. de.wikivoyage, it.wikiversity) is not working yet. What happens instead, is that the link is interpreted as a link to the language's Wikipedia. This affects the file page itself, but not the history.
As an example, on de.Wikivoyage there are 669 files on de.wikivoyage.org, out of which 197 contain links to other pages of the wiki.
Currently, not all sister projects are set up to use FileImporter (see the existing config files here)
- Also non-en-wikis of non-Wikipedias get correctly prefixed.
Probably we could get the interwiki links from mediawiki, see also previous work and investigations:
After this is solved we could also get rid of the articifical config that whitelisted how to resolve specific paths