"Our cats are reading newspapers."
Translation:Unsere Katzen lesen Zeitungen.
Indeed. If this used only useful sentences, you'd probably start to recognize instead of actually learning. This way, if something shocks you, you look twice before sending and it gets clearly into your mind. Also, many of this sentences are not as useless as they seem as they would be quite ordinary in fiction or artistic media.
"Kater" only refers specifically to male cats, as opposed to female ones being referred to as just "Katzen"
I think there's also a word for a female cats, which is "Kätzinnen" but I'm not sure how common it is. If I really wanted to distinguish male and female cats in a clear and precise way, I would just use more explicit terms like "männliche Katzen" (male cats) and "weibliche Katzen" (female cats).
Also, "Kater" has another common meaning, which is "hangover"