As suggested at https://www.mediawiki.org/wiki/Topic:Vqb5rxhirrw0mnh1, it would make sense (and avoid duplicated work) to reserve the rights to a translation not to one article in the source language, but to all language versions that are connected through the corresponding Wikidata item.
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Rather than blocking more, the plan is to make users aware of other efforts as captured in T263357: Connect preemption rights for translation to Wikidata item