I know there are many translations but these two will illustrate my question.
The last line literally means “Sound of water,” but is it generally understood that Bassho meant to imply “Plop,” and onomatopoeia was simply missing from Japanese vocabulary (or the ideogramatic lexicon) at the time, or did he mean to distance the meaning a step from the direct onomatopoeia?
Japanese is rich in onomatopoeia (there are wholebooks on the subject). They use it more frequently than we do in English and in situations where we would think it sounds childish.
The Japanese word for “plop” would be “bon”. I don’t know really know anything about Basho or his time period specifically but I find it difficult to believe there wasn’t an onomatopoeia word he could of used if he had wanted to do so.
I think that he’s leaving it to the reader’s imagination as to what is heard, and I’m extrapolating this idea because in many of his haiku, descriptions of sounds are completely general: bells ring; birds sing; insects sing; etc.
I know of an entire book of 100 different English translations of this poem called One Hundred Frogs.