Translation:We have seventeen more sandwiches.
Yes and no. My experience is that steeds is a word added to share the feeling of emphasis on the word still. Both mean still, but steeds emphasizes what or who is still there for some reason (ie: annoyed that there are nog steeds 17 sandwiches or glad there are nog steeds 17, vs simply there are nog 17 sandwiches, for no particular reason). ☺
Something just does not compute. I believe...we still have seventeen sandwiches..should be the correct translation, however...still..is not a given option in the new word availability format. Does...nog zeventien...convey “that is all there is”, or “still an additional seventeen”, which the ...more sandwiches...implies.
These little words tend to be hard to translate, but nog roughly corresponds to still. So a more literal translation would be "We still have 17 sandwiches." But still implies a certain amount of stress which nog doesn't. In situations where you would prefer that English sentence, you would probably prefer nog steeds in Dutch. Steeds means ever, always (used in a context of continuity), so this is basically a duplication for clarity or emphasis.
There is a difference in English between 'We have seventeen more sandwiches' (ie we had some sandwiches previously), which is accepted and 'We still have seventeen sandwiches' (ie we had seventeen to begin with and they're still there!). Can anyone tell me what the Dutch is trying to convey here?
Unfortunately these little details of idiomatics tend to be slightly tricky to translate even between languages that are very close relatives, like English and Dutch. Here the issue is the difference between nog and nog steeds, as explained in Lenkvist's comment. (Currently the second comment on this page.)
You want to know: Why is "We have more seventeen sandwiches" wrong?
"More seventeen sandwiches" is not correct English at all. It sounds as if you are not sure whether to say "seventeen more sandwiches" or "more than seventeen sandwiches" -- two quite different meanings.
Perhaps you are confusing this with this alternative way to express "seventeen more sandwiches": "another seventeen sandwiches".