Translation:What do you still want to buy?
"What do you still want to buy?"??? This is a very unnatural thing to say in English
You are correct and I understand that it now accepts "what else do you want to buy" which is what we would more often say in English.
But it is also important to realise that 'else' is not always a synonym for 还 (hái) because it means all of these things:
still / still in progress / still more / yet / even more / in addition / fairly / passably (good) / as early as / even / also / else.
You have to add a 吗 at the end. This will turn the 什么 into "something" since the 吗 will take over as the question word (or particle perhaps).
你想买什么 - what do you want to buy 你想买什么吗 - do you want to buy something
(I should mention that I am not a native speaker.)
"would you like to buy something else" was rejected but I think it's fine
Just keep practicing, cheat by getting it wrong and looking at the answer and trying again. All the variations of meaning will congeal after some time. :)
I also went for that answer but in retrospect I am wondering if that would require the question particle ma.
Something needs to be fixed here. My answer was exactly the one the system says is correct, but it was graded incorrect.
The correct answer given as "Do you still want to buy something?" and "still" was not given as an option!