"June and July."
Translation:Mis Mehefin a mis Gorffenaf.
Is it a typo when 'mis' has initial capitals when not starting a sentence, or is it a matter of personal preference?
I believe that it is a typo, but I can see why some people might capitalize it.
You don't have to say Mis in front of each month, Mehefin a Gorffenaf will do.
Though then Mawrth could perhaps be misunderstood as "(planet) Mars" rather than "March" (or "Tuesday"?) ?
Wondering whether the month of July is spelled two ways with a single or dubble n
No, only double n is correct.
As far as I know, the course maintainers have corrected the ones that had the wrong spelling (single n) where they could, but Duolingo has a problem that causes deleted sentences to still appear some of the time, so you may come across ones like this one that have the wrong spelling.