"Gwirion" should be accepted as a translation of "stupid". "Meicrodon" is another Welsh word for "microwave", "hogyn" is another Welsh word for boy; and "hogan", "geneth" and "merch" are Welsh words for "gril". As the above comment correctly points out, "merched" means "girls", rather than "girl".
It's been said by the others, but dude, Merched is plural. And all the other meanings should be looked at. There are so many ways of saying girl and stupid etc. Good otherwise though
merched should be changed to merch, stupid should also accept gwirion or dwl microwave should also accept microdon and there is no welsh word for hufflepuff.