"Cúig phráta, le do thoil."
Translation:Five potatoes, please.
Nouns following numbers stay in the singular form. As well, following certain numbers, the noun is either lenited (1-6) or eclipsed (7-10) (and the same pattern with the teens and so on - lenition on 11-16; eclipse on 17-19; no change on 20; lenition 21-26; eclipse 27-29).
If you're using the desktop version, there is info in the tips and notes section for numbers. Here's a link to the page: https://www.duolingo.com/skill/ga/Numbers
There is a Russian anecdote from 70-90s almost about the same. First of all - the russian student was considered then as poor and therefore hungry. So, the story: The student came to students' diner and ordered 5 sausagies. Everybody around - wow, you became rich. The student overs his order with - ...and 10 forks.
We do love our spuds in Ireland (Spuds should be accepted as well as potatoes).