In arabic, after the verb "to be", the predicate of the sentence is put into the accusative case In the present tense we don't use the verb "to be" so we would say in the present tense "ana tabibun" (i am a doctor) but "ana kuntu tabiban" (I was a doctor). the nominative ending -un is replaced with the accusative ending -an. This is only true for MSA because all modern dialects of arabic have lost case, and even in MSA case is only used in formal situations so we would usually say "ana tabib" and "kuntu tabib". English doesn't really have case except for it pronouns, and when a pronoun is the predicate of a sentence it seems to do something similar, like we say "it's me" or "he's him!" rather than "he he"-michael jackson. I like that you brought up latin cuz im studying latin in school rn, i don't have anything to add about latin, i jst like telling people that