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"Pera pera （ぺらぺら）" is a (words mimicking states). They directly express states or actions of people and things. There are a few meanings for "pera pera" depending on the context.
(1) Talk fluently
Kare wa nihongo ga pera pera desu.
He speaks Japanese fluently.
(2) Talkativeness in a negative sense or to chatter.
Hiroshi wa himitsu o pera pera hanashite shimaimashita.
Hiroshi was so talkative that he told the secret.
(3) Thin, flimsy
Kono shatsu wa pera pera da.
This shirt is flimsy.