English name   Irish name       Genitive
Wikipedia      Vicipéid         Vicipéide
Wiktionary     Vicífhoclóir     Vicífhoclóra
Wikibooks      Vicíleabhair     Vicíleabhar
Wikiquote      Vicíshliocht     Vicíshleachta
Wikisource     Vicífhoinse      Vicífhoinse
Wikispecies    Vicíghnéithe     Vicíghnéithe
Wikinews       Vicínuacht       Vicínuachta
Commons        Cómhaoin         Cómhaoine/Chómhaoine *
Meta-Wiki      Meta-Wiki        Meta-Wiki
  • When it's used in the genitive, Cómhaoin will change its spelling depending on whether it follows a masculine noun or a feminine noun. If it follows a masculine noun, it becomes "Cómhaoin". If it follows a feminine noun, it becomes "Chómhaoin". For example, Commons talk is "Plé Cómhaoin" because "plé" is masculine. But I'm not sure whether this even matters yet seeing how "Commons" is the sitename in use!

For reference, the same might apply to Meta (ie masculine genitive: "Meta-Wiki" feminine genitive "Mheta-Wiki").