Translation:Do you need milk?
When the voice said necesitas leche, there was no inflection to indicate that it was a question. How are we supposed to know without any written indication or voice inflection that it is a question versus a statement?
The "s" ending "necesitas" implies "you." Pronouns are often omitted in Spanish, but almost in English. Your translation "Need milk? is an exception.
DL might accept your translation if you submit it, but I doubt they will.