The sentence that is written correctly is: Walt Whitman’s poems express an amazing “joie de vivre.”
This is so since "joie de vivre" must be written in quotation marks, as it is a foreign expression (in this case, from the French) that must be translated to be understood. Its translation is "joy of life".
When a foreign expression is used in a text, it must be clarified with quotation marks, to make the reader understand that it is a foreign literalism, and not an expression that is unknown to him.
