There may be an issue with the translation tool, which allows to translate articles form one language to another. When the translation is published, the interwiki links for that language should be added (or handled by wikidata).
Look at the highlighted sections in the screenshot below: I just "translated" Parson's Cause" from English to Simple English, I am viewing the page on SEWP for the last corrections. The software shows the available translations/pages in other languages/wikis, but lists SEWP as absent (from WikiData).
First of all: I am editing in SEWP, so "Simple English" should not show up at all there. Secondly, "publishing" a translation should also add the corresponding WikiData entry.