"They have trousers on."
Translation:Tá brístí orthu.
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Well, seeing as English is not my native language, I wouldn't be 100% sure, but I would personally lean towards "they have a hat on".
But anyway, there's a few languages I'm aware of where it would unequivocally be "they have a hat on". So my question would be whether Irish is in the first or second group.