"Ní mhothaíonn siad."
Translation:They do not feel.
"Feel" in what sense? I sometimes think that the single-word definitions that Duolingo gives are too simple because the words they give as definitions can mean so many things––not to mention that they can be transitive or intransitive.
I would have to disagree, and call the official translation here incorrect (and am not able to imagine what the constructor of the Irish sentence had in mind). There is no way that — in English — you can just "feel". There needs to be a stated complement. You can feel something (perceive it, perhaps physically), or feel some way or some how (e.g. hungry). When using feel to express an opinion or sentiment (about a poem, say) a complementary clause must follow, perhaps introduced by "that".
To say "They do not feel." in English means that the subjects have no feeling, whether in the physical sense that their nerve endings are dead, or the metaphorical sense that they are callous and without empathy. I have no idea how old this comment is because mobile doesn't display a date, but I still felt like clearing this up.