One of the key requirements for the position is fluency in both spoken and written Japanese.

fluency 是名词，来自形容词 fluent（流利的），加上名词后缀 -cy 构成。fluent 本身来自拉丁语 fluere（流动），比喻语言表达像流水一样顺畅自然。fluency 指"流利程度、熟练程度"，特指语言运用的自如程度。