There's really no room for interpretation. The official pronunciation is correct, and any others are not.
Yes, it was definitely a mistranslation. Kingdom Hearts is correct calling her Aerith.
No, it was NOT a mistranslation, and Kingdom Hearts only called her Aerith as fanservice.
I'm really indifferent on the matter.
*Poll Option Under Construction*
There's really no room for interpretation. The official pronunciation is correct, and any others are not.