This is fixed by localisation updates removing {{formatnum}} from the translation for this string.

https://gerrit.wikimedia.org/r/#/c/23750/1/repo/Wikibase.i18n.php

{{formatnum}} still appears in another Farsi string:

wikibase-propertyedittool-counter-pending-tooltip

not sure why it's used there, and it's not used in the corresponding English string.

underlying cause is that there is no {{formatnum}} functionality yet in MediaWiki's JavaScript, but otherwise translators might use it and it can be used in php messages.

Not sure translators are aware of such things, nor is it clear which messages are JS messages in the i18n file or translatewiki.

Verified in Wikidata demo time for sprint 17