Well, the first problem is the "wrong" translation and interpretation of the word
news between languages. The word stands for
NEW thingS (NEW_S) and shouldn't be translated with "Nachrichten" but with "Neuheiten" instead. "Nachricht(en)" would translate to "message(s)".
So we use different words for the same Action.
Watching the news. --> Die Neuheiten ansehen. (valid, but noone says that in Germany)
Watching the messages. --> Die Nachrichten schauen.
So the 2nd problem is the interpretation and/or the "comon toung"/dialect.
Also, always keep in mind, that German and Enlish are mostly (~90%) the same languages with the same words. Dont fully rely on only one Website or one translation, and look for an simillar translation. For example:
Car --> Auto
is accpeted and mostly right, but its not the correct translation of the word
car. That would be
Car --> Karren
wich would mean
cart. But since everybody knew carts and wagons before "Cars" where a thing, the "common toung" named the new vehicle "car(t)" or "wagon" aswell, hence the name "Volks-Wagen (VW)" or "Kübel-Wagen" in German. We also still use the word "Karre" and "Wagen" in a sloppy way/dialect to describe a car. ("Automobil" / Autoum Mobile)
And as you noticed, neither of both sides got the real word (latein or greek) correct, since it means "moving on its own" and would be (and in fact is) in both languages the same, untranslated word. Car, cart, Karre(n) and Wagen are nothing but synonymes for the same thing.
Hope that makes things a bit clearer, since RDBury's answer is mostly wrong or "to easy".
So to answer the question of plural vs. singular - in fact, it's the english phrasing that is wrong/common toung. You are adressing the plural of "new (thing)", so
"new (thing)s" with an is.
The correct sentence would be either:
This/These are bad news. --> Das sind schlechte Neuheiten/(Nachrichten).
This is (a) bad new (thing) --> Das ist (eine) schlechte Neu(-heit).
It's yust an exception, mostly because of the interpretation, dialect/common toung and word-shifting over the last years. The normal Plural- and Singular-Forms/Rules apply to all german words the same.
In fact, to confuse even more, its one of these wierd Plural-Form-Exceptions:
1 Fish, 2 Fishes
would be correct, yust like dish and dishes, but for some reason
1 Fish, 2 Fish
is accepted and used. So even though the english language has and can form the plural of Fish without problem, its never done.