An opinion on translating terms from Japanese to English
My hot take as a consumer of translation: it's possible for a translated term to be accurate & faithful and also be a bad translation.
It can even be a bad translation if the word of god from the creator is 'this is what it's supposed to be in English'.
A great exhibit for 'the word of the creator is sometimes wrong' is the official title romanization of Miyazaki's Castle in the Sky.
I believe that Miyazaki himself is on record as wishing that he'd known more at the time and officially romanized ラピュタ as 'Raputa'.
Miyazaki famously named the city in the sky (and the film) after the flying island from Jonathan Swift's book, and because he did so he was very clear that the proper romanization was of course 'Laputa', which is what Swift was using. What Miyazaki didn't know at the time he made the romanization choice is what Swift was probably alluding to with the island's name and what it means in Spanish.
I'm reasonably convinced that 'sleigh beggy' from The Ancient Magus' Bride is another unfortunate translation choice, tho it's not clear.
I say it's not clear because I haven't found an authoritative reference for what the original Japanese version of the phrase/term is. There's a formal title that translates more or less to 'Beloved Child of the Night' (cf), but I don't know if there's a short informal term used for it in the original manga.
(I suspect there is but I don't know for sure.)
When you need to immediately redefine what your translated term means, something has gone wrong. Cf <link>
A 'sleigh beggy' is a relatively obscure type of fairy from English folklore (specifically from the Isle of Man). However, this is not what the term means in the context of The Ancient Magus' Bride, where it instead means a special type of human. That Seven Seas had to immediately redefine the existing term this way is, to me, not a good sign.
(Yes, sure, 'sleigh beggy' is likely obscure except to people deep in English folklore. The problem with the Internet is that explanations of puzzling, obscure things are only an search away, ready to mislead you in this particular context.)
I could also rant about 'Maho Shojo Madoka Magica' officially turning into 'Puella Magi Madoka Magica', but that's a tired subject by now.
The short version of the rant is that the connotations of 'Maho Shojo' to a Japanese audience are completely different than the connotations of 'Puella Magi' to an English audience. One is a common, well known, specific genre reference, the other is a Latin phrase used by nothing else. And the genre reference is very important to the show in context, since Madoka is built on and is riffing on magical girls shows.
Yes, 'Puella Magi' is the official translation by SHAFT (as far as I know). That doesn't magically make it a good one.