"The plates and the pots are dishes"
Translation:Sahani na sufuria ni vyombo
They're both N/N class nouns (class 9/10) so their plural is identical to their singular.
Other words that refer to them may give it away:
sahani yangu = my plate
sahani zangu = my plates
But in this sentence, it's just context. It could also mean "a plate and a pot" or "the..." etc.