Je ne sais quoi 不可言说
Je ne sais quoi is something that cannot be adequately described or expressed.
不可言说指无法用语言充分表达的某物。
Je ne sais quoi是法语“我不知道是什么”的意思，这个词表达的不可言说之物多为褒义。
Example：
Although the sculpture had flaws, it also had a certain je ne sais quoi that made it very appealing.
尽管这尊雕塑有瑕疵，但某种无法言说的东西赋予了它魅力。