Shouldn't "One leu, two leus" be accepted as well?
No, because that's Romglish, not Romanian.
Then what would you call the Romanian/Moldovan currency in English?
Lei! (Or in commerce RON - for Romanian New Lei, as opposed to ROL, the old Romanian Lei before revaluation.) Bulgaria also uses lions for currency - Bulgarian Leva (лев is the old Bulgarian word for lion.)