"We have not heard the wolf."
Translation:Nie usłyszeliśmy wilka.
In English you use Present Perfect so in Polish you should also use perfective form of the verb: "słyszeć" (imperfective) -> "usłyszeć" (perfective). Perfective verbs express that something was done/action was completed. So depending on context, "Nie usłyszeliśmy wilka" can be translated either as "We didn't hear the wolf" (when the action happened in the more distant past) or as "We have not heard the wolf" (if the action happened in the nearer past or we want to accent its influence on the present situation). On the other hand, imperfective verbs accent that something lasted and say nothing about the effect so in this context such translation would be rather not precise because we wouldn't express the same idea like in English Present Perfect.
If I understand English correctly, We have not heard the wolf is about consequences of the past finished action in the present. Polish słyszeliśmy is about past unfinished action , and usłyszeliśmy about past finished action.
Which makes me believe that the best way to translate we have not heard with * nie usłyszeliśmy*.
While we did not hear wolf / we were not hearing the wolf is nie słyszeliśmy wilka.