Rascal doesn't start to speak like Irish (5)

I believe the answer is:

rogue

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'rascal' is the definition.
(both can mean a scoundrel)

I don't understand the remainder of the clue.

(Other definitions for rogue that I've seen before include "Mischievous person" , "Bad guy" , "Scallywag" , "Old Greek" , "Diseased plant" .)

I've seen this clue in the Sydney Morning Herald.

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