Hi Dirk
This will get all the nested tables regardless of their depth, although I am not certain whether this or the Grep method would be faster for very lager documents with large amounts of nested levels.
var doc = app.activeDocument, t; (t = doc.stories.everyItem().tables.everyItem()).tableDirection = TableDirectionOptions.RIGHT_TO_LEFT_DIRECTION; while (t.cells.length) (t = t.cells.everyItem ().tables.everyItem ()).tableDirection = TableDirectionOptions.RIGHT_TO_LEFT_DIRECTION;