Spaces in the interwiki link can make it into interlanguage link. For example [[:en:ox|ox]] is a proper inline interwiki link, with word "ox" linking to wikipedia article, but [[ :en :ox|ox]] (with spaces) does not show in the text, but rather shows up as a interlanguage link in the side bar on the left.
|mediawiki/core||master||+17 -1||Parser: Trim leading whitespace from links before checking for leading :|
I just tried:
- [[ :en :ox|ox]]
on English wikipedia and it was parsed correctly (the same way), but Commons, Polish Wikipedia and Wikidata parses them differently. So maybe it is just the matter for all the project to use the same Wiki text parser as English Wikipedia.
I just tried
[[ :en :ox|ox]]
on Commons and on English and Polish Wikipedia and the first 2 parsed correctly, but the 3rd one did not. So it looks like 2 spaces option works fine now but the second space option is still wrong.