"esprit" is one of those semi-untranslatable French terms that carries a huge load of cultural import. In the context of Franco-American relations, and given the great weight traditionally placed by the French on ratiocinative capabilities, "intellectual capacity" seems to me the term that best conveys the intended sense of your phase.

(Alternatively, and much more colloquially, you could say "...They're not stupid, but....")

Cheers, HC

They may well be intelligent, but they are lacking in spirit.

Many possibilities. As suggested by Heathcliff, the meaning may extend to "intellectual capacities", although it may in fact mean to say "they lack imagination".

Nikki

Esprit should really be translated as "witty" but that will sound outdated at this point, unless you're dealing with an older text of course...

in light of the other answers I began to wonder what the French word "esprit" could cover. Result? Just about as much as in English, if not more! If the translation of the word “esprit” is what is really at issue, then this may help (Nouveau Petit Robert) :

“la réalité pensante”
- le principe pensant en general
- principe de la vie psychique
- ensemble des dispositions, des façons d’agir habituelles
- principe de la vie intellectuelle

“aptitude intellectuelle”
- aptitude, disposition particulière de l’intelligence”
- qaulité, valeur intellectuelle
- vivacité piquante de l’esprit

Et aussi
- attitude générale qui determine, oriente l’action
- fonds d’idées de sentiments qui orientent l’action d’une collectivité concrete ou abstraite
- le sens profound d’un texte ; l’essentiel de la pensée d’un auteur

After that, I turned to my English thesaurus, which gave me as many possibilities.

Conclusion? Stick to "spirit"!

Nikki

or witless intelligence. No native critical spirit.

or
They are intelligent, but they don't have wit
or
They are intelligent, but not cunning.

I prefer using the word "wit", I think it's what best describes the word "esprit"
(using "wit" in the sense of:
3 a : astuteness of perception or judgment : ACUMEN b : the ability to relate seemingly disparate things so as to illuminate or amuse c (1) : a talent for banter or persiflage (2) : a witty utterance or exchange d : clever or apt humor
4 a : a person of superior intellect : THINKER b : an imaginatively perceptive and articulate individual especially skilled in banter or persiflage)