I would agree that the given translation "He is not personal" doesn't make much sense. But "It is not personal" does make sense, and that's how you'd say that in Irish.
True, however "é" is also "it". As someone else pointed out, the sentence also means "it isn't personal".
No, é doesn't mean "it". Sé and é can both mean "he" or "it" depending on context. Strictly speaking, Irish doesn't differentiate between "he" (or "she") and "it", you just have to pick the appropriate translation when translating to English.
Is múinteoir é - "He is a teacher"
Is bosca é - "It is a box"
Tá Pól ag siúl. Tá sé ag dul go dtí an stáisiún - "Paul is walking. He is going to the station"
Tá an bus ag teacht. Tá sé ag dul go dtí an stáisiún - "The bus is coming. It is going to the station"
Whoops, that's a typo, should be "sé" can also be "it". I'm aware of the non-differentiation in Irish -- I'm assuming that "it's not personal would' also be accepted for this?
It should be, as that's how you'd say "it's not personal", but it's been a long time since I got this sentence, and I can't remember what Duolingo accepted.
Why do I use the copula in a sentence like "Ní fior e" but not here?
Yes, it would.
to take sth personally
glacadh le rud go pearsanta
rud a thógáil go pearsanta
"don't take it personally" - ná glac go pearsanta leis