fluently (speaking a foreign language)
incessantly (speaking); glibly; garrulously; volubly
one after the other (flipping through pages)
thin (paper, cloth, etc.); flimsy; weak
彼は英語がぺらぺらだ。
He speaks English fluently
日本語がぺらぺら話せるようになりたい。
I want to become fluent in Japanese
三年でぺらぺらになった。
I became fluent in three years