"숲에 늑대가 없어요."
Translation:There are no wolves in the forest.
You're probably right, since the rules for making plurals of English nouns ending in F are not straightforward. (Either just add S or drop the F and add VES [and some words such as "dwarf" can go both ways]. Unfortunately, you have to memorize which words go which way.)
"Wolfs" is a real word, by the way. It is the third person present tense form of the verb "to wolf", meaning to devour (food) greedily. "Instead of taking her time to enjoy it, she wolfs [down] her breakfast every morning."