Hi,
Is the following sentence correct?
'I don't know what's his acquisition criterion' In French : 'Critère d'achat'.
Achat and acquisition have almost the same meaning. The former can be used for shopping and commerce too. Since the phrase is used in a seemingly technical context, we'd better find the exact concept. If it's about language or psychology critère d'acquisition can be good, because we say l'acquisition des langues.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.