Translation:dydd Mercher, dydd Iau
Oh poo, I forgot to add 'dydd'...so it just can't me on its own at all, the days? mercher, iau?
Actually you will seen them without dydd but only if you are referring to the night of that day in which case you say "Nos _" with the dashes being one of the day names. Note that because Nos is feminine certain days mutate softly after it so "Nos Lun", "Nos Fawrth" "Nos Fercher" "Nos Wener". Iau, Sadwrn, and Sul don't mutate because "i" and "s" are not letter that mutate