"May I have that pan, please?"
Translation:Ga i'r badell 'na, plîs?
why wouldn't the full form of 'hwnna' work here (or 'hynny,' 'honna')?
It would either be "Ga i'r badell 'na" or "Ga i'r badell honno". "Hwnna" and "Hynny" don't work because they are the wrong gender for "Padell" (Which is a feminine noun") and "Honna doesn't work because we don't use it in this consturction instead we use "Honno". It's best to stick with "'na" for personal use though since it's a lot easier to use and it's what you'll come across in everyday life. Also "'na" isn't a shortening of "Hwnna" or "Honna" it's a contraction of "Yna" (There).