leaving out "ni"
The course translates "Chakula kitamu mno" as "The food is too delicious" https://forum.duolingo.com/comment/24538052/Chakula-kitamu-mno
I think this is the only time I've seen a sentence like this without "ni." Is it common to leave it out? Can you only leave it out when the predicate is an adjective vs. a noun? Or should this actually be translated as a phrase, something like "food that is too/very sweet/tasty/delicious"?
(Incidentally the version with "ni" also appears in the course: https://forum.duolingo.com/comment/25316955, and for that same exercise in the opposite direction https://forum.duolingo.com/comment/29569722 "Chakula kitamu mno" isn't accepted.)
It is common to leave out the "ni" in conversation, especially in simple statements or questions, as long as it does not cause confusion. So you might hear "Jina lako nani?" instead of "Jina lako ni nani?" or "Yeye mzuri." instead of "Yeye ni mzuri." The "ni" provides emphasis (and maybe grammatical correctness, depending on your point of view). I think it will be a long time before DL Swahili consistently includes this variant of leaving out the "ni". But there should be no penalty for using "ni" in the type of sentences mentioned above.