“Yada, yada, yada” is an early 20th century equivalent of “blah, blah, blah.” It is American, and emerged during or just after the World War II. The alliterative saying was preceded by various alternative forms – “yatata, yatata,” “yaddega, yaddega,” et cetera. An example is found from an advertisement in an August 1948 edition of the Long Beach Independent:
“Yatata . . . Yatata” . . . The talk is all about Chatterbox, Knox’s own little Tomboy Cap with the young, young come-on look!”
Fig. It. Out.