Zatara first appeared in Action Comics #1 (June 1938), sharing the issue with Superman, casting by backwards incantation from the start; Zatanna arrived in Hawkman #4 (1964). Real-world parallels are documented: reversed words and voces mysticae run through Greek magical papyri, the Ephesia grammata, Kabbalistic letter-mysticism, and the Victorian stage magicians Zatara was modeled on.
The backwards mechanic does story work: it makes magic a language with grammar, rules, and costs, which later writers, notably in Justice League Dark, built into cosmology where language stabilizes a force older than the gods. Zatara teaching his daughter that magic always has a price is the strip's one unbroken law.
Occult readers note that the comics' rationalization matches the traditions it borrows: true names, inversion as power, speech as the lever that moves reality. On that reading, Zatanna's gimmick is the most honest depiction of operative word-magic in mainstream fiction, played as vaudeville.
Backwards speech as the engine of magic: random gimmick, or a folk memory of every tradition that said the true names of things run underneath ordinary speech?