I wrote "A man, woman, girl and boy." and it said I was wrong, but in English it's okay to use one indefinite article in the beginning of a list if all the things in the list use the same one...
That's not a terribly helpful answer. If the translation is correct then it should count it as correct, but it counted it as wrong, so it should be fixed. It seems from a reply further down that it has been corrected.
I'm a beginner too, but from what I understand, pronunciation and phonetics in Celtic languages differ immensely from those in Romance or Germanic languages - "broad" and "slender" consonants, glide vowels - like "ea" in "fear" being pronounced as "farr" - and a fun little trick "h" does where it isn't actually a letter, but a function which changes how consonants around it are pronounced.
In this case, it may possibly have to do with the initial consonant sound of the words... or it could be a quirk that one just has to get used to - unintuitive as it all may sound to Sasanach ears.
Keep at it!
Of course, the 'h' is down to difficulties in producing diacritics in typing. Originally, the lenition was shown by putting a dot (séimhithe`* not sure if it's standard but pronounced by my mother as 'shave-ih-huh') above the consonant (which goes back to Latin, it was the equivalent of crossing a letter out). bh, ch, dh, fh, gh, mh, ph, sh th should really be something like ḃ, ċ, ḋ, ḟ, ġ, ṁ, ṗ, ṡ, ṫ respectively. It looks better on the insular script. I suspect that's why the top of the B and D slope down and the F, G, S, and T have flat tops. It's not as pretty but it's easier just to tack on a 'h'.
Plenty of people don't. I think it's the people who programmed it, rather than the Irish language itself. But, for this sort of sentence, the Oxford comma doesn't make too much of a difference, so it's fine either way. It's only when the sentences can get ambiguous that it really makes a difference.
I typed it with one and it accepted it, so whatever works, I guess.
Had a laugh here; don't know if anyone else is experiencing this - my Mac seems to know which language you're typing in and throws a red line under spelling errors. Works with all the Duo languages so far. Tonight finally introducing it to Gaeilge, and everything's getting a red line, incorrect or not. Computer's confused :)
I use predictive text on my phone so I can kind of cheat on spelling if the keyboad for that language is supported. And for Romance languages, you can often do a vague shape (swype-like input) of the English word (e.g. intelligence) and it will just write the Spanish word (inteligencia) anyway. On the Irish course, I don't have support for Irish so I have to type letter-by-letter. Which is probably better because Irish spelling is something I definitely need to get the hang of.