I think this question here was originally too unclear.
because I was still researching and figuring out exactly what I wanted to ask when I posted it.
I edited it a few times,
but I think my editing has changed the question enough that it's no longer clearly the same question as when I first posted it,
so I decided I should probably post a new, separate one.
I make sauerkraut with 20 grams of salt per kilogram of cabbage.
Is the proportion different for pickling lemons/limes?
I would guess maybe lower because of the citric acid already there...?
I found one site saying 5~10% for "North-African style",
which is what I think I'm going for.
(I used to get them at Morrocan stores,
but the city I live in now doesn't have any.)
But if that "5~10%" is really by weight in the same way,
then that's a lot more than the 2% for sauerkraut,
which is surprising and confusing.
Also, I don't add any water to my sauerkraut,
but maybe that's necessary for lemons/limes?
In which case I would just salt the water at the same salt/water ratio as the salt/fruit, I assume?
The ones I used to get, I'm not sure, but I think they used nigella.