He has that je ne sais quoi that distinguishes a professional from an amateur.

他有那种难以言表的特质，体现出他是专业而非业余的。

If they are both bad, she comforts herself that she has graces; a certain manner; a 'je ne sais quoi, ' still more engaging than beauty.

假如她的容貌和身材都不好，她就会相信自己具有魅力，具有某种“难以描述的”、比美貌还要迷人的风度。