idiomatically

He speaks English so idiomatically that people often forget it's his second language.

(Chinese) 他的英语说得如此地道，人们经常忘记那是他的第二语言。

The phrase 'kick the bucket' is idiomatically used to mean 'to die'.

(Chinese) ‘kick the bucket’这一短语在习语用法中意思是‘死亡’。