How do Brits and Americans pronounce pain au chocolat?
In the UK it depends on the speaker but I would say the most common way is "pan oh sho-coh-la", with the stress on the "la".
With foreign words I use the nearest English sound. I don't try to make foreign sounds when speaking English - I think it's pretentious.
In coffee shops, you sometimes hear pain au chocolat or pain aux raisins pronounced as if the last word is the corresponding English one - especially in one chain which spells the second one "pain au raisin". I think what's happening there is that the staff are mistaking it for the original English word, rather than recognising it as part of the borrowed name of the pastry. They will confirm your order by saying "a panno chocolate".
In Britain, I think it's normal to use (at least an approximation of) the French pronunciation.
To address your point about why many more people anglicise "croissant", I think there's a distinction between words adopted from other languages, which often get anglicised, and phrases, which tend not to. Since none of the words in "pain au chocolat" has passed into English individually, it's still a French phrase.
French speaker here, living on the US East coast. It varies: they usually try to say it the French way, which is close to "pen" or "pan". I heard once "pain" as in "painful" and it was hilarious.
It should be something like "pen/pan oh shockohlah". Americans like to emphasize the "shock" instead of the "lah".
Americans don't seem to mind or be offended if you try to pronounce it the French way.
As an American expat in the U.K., my experience has been pretty well in line with the other answers here. One interesting addition I might make is that Americans as often as not just won’t try to pronounce French words. Foreign language words that cannot be replaced easily become an Americanized replacement.
If you do encounter an American who makes the effort to properly pronounce this (or any other foreign language word), another American will hear it as either
- incredibly pretentious (if pronounced correctly) or
- comically wrong (if pronounced wrongly)
For my part it took me some time to acclimate to ordering a “pain au chocolat” after I moved to London. I only ever ordered a “chocolate chip pastry” as a child, even when I was visiting Versailles, PA (pronounced Ver-sales) or Des Plaines, IL (pronounced dess planes).