Mosogat is better translated as "wash up", which means "wash the dishes". This should be included as an acceptabel option.
In some ways.. "wash up" is truly the best option here because "mosogat" doesn't mention a "dish" anyway, only implies the presence of dishes, in the same sense as "washing up" or "doing the washing up" in English implies the dishes etc but never specifically states what is being washed.
Sometimes it feels stupid adding "dishes" when translating this verb, almost as stupid as trying to invent / choose a "he" or "she" for the English translation when "Ő" is used, or a third-person singular verb that needs such a pronoun in English to go with it..
We use "they"--the singular plural--to avoid gendered pronouns these days. http://www.oxforddictionaries.com/words/he-or-she-versus-they
Yeah; I know .. and that feels to me the most logical, intuitive, almost perfect way to translate "Ő", but: I've given up on trying to use that in Duolingo Hungarian though, because it is never accepted! (or has that changed? So far it has rejected it each time I tried to use it :) )
You are quite mistaken. Both are used in UK English. This is just splitting hairs over nothing.