Non-admins can create and translate MediaWiki pages used in Wikidata interface using Translate Extension. I, User:4nn1l2, am not an admin on Wikidata, but I could create MediaWiki:Search-nonefound/fa and Translations:MediaWiki:Search-nonefound/1/fa.
It is worth mentioning that this is not possible on Commons. I also tried to do the same on MetaWiki and Mediawiki.org, but I could not find any appropriate messages.
The issue was originally reported at Commons translations' noticeboard: https://commons.wikimedia.org/w/index.php?title=Commons:Translators'_noticeboard&oldid=336435626#Translation_capability