"Do you want to slice the onions?"
Translation:Вы хотите нарезать лук?
FYI: in such cases we usually use the negation, the particle ли and slightly different word order: не хотите ли вы нарезать лук?
So in what cases is it treated as such? The fact that plural forms of the word exist indicates that sometimes the plural would be used.
E.G. in English, both "hair" and "hairs" work regarding more than one hair, but they have different uses.
Also, could луки be used here regardless of its mass noun status? Perhaps it would simply sound unnatural and awkward, like saying in English "I am going to chop the fishes for dinner".
It's always a mass noun when it means "onion". The plural form exists only for its homonym "лук" wich means "a bow" (a weapon). So "луки" can only mean "bows", not "onions", therefore you can't use it here.
(Well, there are also some other homonyms for that word but these two meanings are the most common ones.)
вы is used when your talking about many people. And ты is used for a single person
Also Вы is used for formal speech for someone you do not know. Ты is informal. You would use the latter when talking to a friend.
Is the verb 'to want' irregular in russian in terms of the verb endings? I would expect it to be something like вы хочете, but duolingo says the correct conjugation is вы хотите
Yes, it's irregular, and not just for 2nd person ч is used in all singular verbs and т in all plural verbs:
(The conjugation table I use adds the mark on the stressed syllable.)
In the conjugation table I use, both Perfective and Imperfective aspects are spelled the same, but the table marks different stress-syllables:
нареза́ть / наре́зать
Which one is being used here, and why, if anyone knows and could be so kind as to illuminate the matter for me?