"Emilian's shirt is nice"
Translation:Shati la Emilian ni zuri
Yeah, I wish there were a way to turn off Duolingo's acceptance of typos.
That being said, the way you said it, treating shati as a class 9/10 noun (N/N) is not a grave mistake and a lot of Swahili speakers treat all inanimate nouns as 9/10. There is quite a bit of movement and disagreement between speakers and dialects between which nouns belong in the 9/10 group and which in the 5/6 group in particular (the (ji)-ma group). Personally, I think the double error, with ya and nzuri is better than making only one of those errors, because what you have done is at least consisitent - you've just assigned shati to a different group. If you had used la with nzuri, or ya with zuri, that's less consistent, even though you're only making one error: the error then would be in your knowledge of the agreement system of Swahili. Your error now is merely to assign the word shati to the wrong class.