American readers really can't adapt to that degree

Well, to be fair, "jumper" is already used in American English, just not for the same article of clothing as it is in British English. I don't think it's that unusual to read a word you already have a meaning for and wonder at its seeming misuse (Harry putting on a jumper, for instance, or the whole "pants" definition thingie). Sure, it's more or less easy enough to work out in context (although I had to hunt down a British person to figure out what the hell a "modcon" was), but I just don't find misunderstandings of that sort to be proof of inability to adapt.

Perhaps it makes me a linguistic isolationist, but I tend to read things through the lens of the meanings of words that I've used all my life.

Sometimes I just skip over stuff I don't understand. I could swear I've never heard 'modcon' before but I'm sure it will jump right out at me next time I see it just like 'chipolatas' yesterday.

I read a lot of british mysteries, so I'm not sure much of the slang would phase me, but Beau doesn't understand at least 10% of the BBC shows we watch.

Fair point.

I think my rampant Anglophile fangirlishness dims my view of the translations because I prefer the 'when in Rome' approach. The minority view...I can accept that.

My vote is still for no translation, glossary in the back. I mean hell, the books were published by Scholastic - if they can't shoehorn in some vocab educational content, who can?

My vote is still for no translation, glossary in the back.

Which just took me to an Anathem place. I did so much flipping back and forth between the text and glossary that it impeded my enjoyment of the book. Though I think a re-read would be much more enjoyable, because I'd remember a lot of the words now.

Normally, I'd vote no translation, but I think the hyphens alone might kill me: [link]

I got used to glossing over terms I don't understand when I read Louisa May Alcott as a kid. Her books are filled with references to people, places, and items that never left the 19th century, and I just learned to go with the flow.

I'm just skimming, but fully 90% of that list could have been left in the British original text for Americans to read with no impediment to comprehension. I mean, really:

Meanwhile, in the changing rooms,

Meanwhile, in the locker room,

And

Quaffle taken by Slytherin

changed to:

Quaffle taken by the Slytherins

both strike me as being a pointless waste of effort.

This might be my favorite

platters of fat chipolatas

changed to

platters of chipolatas

I think if you are a Br-Am English translator (and I did know someone who did that), you do everything. I know that, as an editor, I make certain changes just because otherwise readers might think we made a mistake.