As usual, I was mentally translating everyday, common things the other day for practice and wanted to say blah blah blah, but I wasn't sure if there was an already established way of saying this in Esperanto. Is there?
- Bla bla — blah blah
- Um um um — mumble mumble
- Babil babil — natter natter
- Klaĉ klaĉ — gossip gossip
I think most European languages use the blabla formula.
The origin of bla, bla is in ancient Greek. The Greek explorers encountered people at the northern shores of the Black Sea and in their ears the local parlance sounded like bar, bar, from which came the word barbarian and the manner how they speak.
Addendum 2019-09-27: Therefore I think bla, bla is quite widely understood.