"The children cleaned the dirty plates."
Translation:ngop lam luSay'moH puqpu'.
Note that the word ngop and its singular counterpart jengva' are part of a small class of nouns that work this way. The plural of jenva' plate is ngop plates, not jengva'mey. jengva'mey does mean something, though: it means plates scattered all about. ngopmey plateses, on the other hand, is ungrammatical, and is an error that some Klingon children are known to make.
Here is a list of some other nouns with irregular plurals: https://en.wikibooks.org/wiki/Klingon/Grammar/Plurals/Irregular-Nouns