About [[MediaWiki:Randomincategory-nopages/ar]]
To allow more localization and to hide the English Category: the message should say: "There are no pages in the [[:Category:$1|$1]] category."
I'm note entirely sure how this allows more more localization (Any language that wants to do so, can already structure the message like that) but I have made the change: https://gerrit.wikimedia.org/r/80311