English requires an article before knife: "A knife is also a weapon." or "The knife is also a weapon."
"Knives are also weapons" should also be acceptable.
Yes, I agree. Also, "That knife is also a weapon." should be accepted.
"Pisau itu" means that knife, so I think you are right and it should be changed.
It's got nothing to do with that “itu” though, “Knife is” wouldn't make sense regardless.
"Pisau itu juga senjata" can also be translated as, kife is also a weapon; without mentioning the "that/itu". Can't we?!
It's like : pisau itu juga senjata lho!
Kife is also a weapon tho!
Yes i confirm that.