Translation:Well then, the bread, please.
I read a manga about the meiji period, apparently bread was used to"cure" diseases caused by white rice for wealthy picky esters. In Japanology or sone other shows, it wasn't until after WWII that Japan Incorporated flour into their diet because America sent lots of flour as aid. And apparently that's the birth of monjayaki and okonomiyaki. But I can be wrong.
Bread is largely a European and South West Asian thing, leading to some interesting names for it in the far East. In Vietnamese it is banh mi, wheat cake if I remember correctly.
The implication of じゃあ is "in that case". So, rather than reminding the waiter, a likely scenario to use this sentence in is when you wanted to order something, but they've run out so you just go for bread instead, or when the shop assistant informs you that they have a special price on bread with every order and asks you if want some.
More accurately, "pan" is a latin root. So yes, the Portugese specifically brought the word, but I think it is more correct to say that the word is written in katakana because it is a latin word, and is the same in most romance languages, Spanish, French, and of course Portugese.
In European countries, bread has been the basic food, since it comes from the wheat, the main cereal here. In America, in contrast, they have got a lot of recipes based on corn, its main cereal (look at mexican "tortillas", or colombian "arepas"). And so, in most of Asia, the main cereal has been rice: just take a look at japanese or chinese gastronomy and see a lot of dishes containing rice, as the main ingredient or just as a garment. Moreover, the japanese "onigiri" are a kind of japanese sandwich but made with rice instead of bread, so we could say that rice was (and is still) the "asian bread" before the cultural exchange between Europe and Asia.
I hear "pan wo kudasai". I was told that をis always read "oh", but apparently there are regional differences and some debate about this. Is it true that people say wo, with a weak w, if the word before ends in n? It's the case of this example and it's suggested here http://yesjapan.com/YJ6/question/769/how_is_really_pronounced
In English, they're both functionally the same, but in Japanese, this sentence is technically a polite request.
It's getting a bit pedantic which is "more correct", but "Well, I would like bread" is more akin to a statement of desire (polite version of "want"). Arguably though, since the request is implicit, it should still be acceptable in certain contexts.
A real question will have the particle か at the end of it.
This statement lacks it because while it looks like a question in English translation, it isn't really functioning as one. It's exactly as if you were at a restaurant, and you told the waiter "could I have the bread please" with the full expectation that the waiter will, in fact, get you the bread. So it's an imperative, rather than a true question. The "please" is just for politeness' sake.
In English you make it sound like a question to be polite, but you wouldn't want the waiter to respond as if it actually were a question -- "Yes, sir, you could," but not go fetch it -- so it isn't really a question. And Japanese has other ways of making the request polite, so it doesn't need to make it sound like a question. Same function, different forms.
Cultural difference. English-speakers often phrase a polite request as a question, while Japanese-speakers basically only use question markers for inquiries that can be responded to explicitly (i.e. with words), not for expressing desire to have something.
Turning this into a question akin to western cultures could be understood as asking for whether or not it is possible, in theory, to have some bread (pretty much any Japanese-speaker would know what you actually mean, it would probably just sound a bit odd and western).
That said, I don't know why they didn't allow "I'd like..." as a valid answer.
As a fellow native English speaker, I agree, and personally I favor translating this as "bread, please" or "~, please" instead.
～をください is a very common and standard way to order food, though naturally, there are also a great many acceptable alternatives of varying politeness. In terms of "class", in my experience, this phrase is most common at fast-food restaurants and cafes. People tend to go for the more polite versions at fine dining establishments, but that's not to say that using ください should be avoided there either.
As many other people have observed, it largely boils down to whatever version of English you happen to be most familiar with.
I believe, at time of writing (May 2, 2018), the Japanese course is still in Beta, so these kinds of inconsistencies are still being ironed out (and taking a while to do so, unfortunately).
Personally I favor translating ください simply as "please", as in パンをください = "bread, please" and さかなをください = "fish, please", but I'm not part of the development team ┐(‘～`；)┌
'Well, bread then, please.' (British English) is not accepted, though the meaning is the same as the (American) 'Can I get...' Which is just not the way it's said here.
I think 'may I have...' should be a translation option, as 'can I get' sounds weird, even coarse, where I live - unless you're speaking with an American accent (in which case we know you're actually being polite). ;)
を is typically called the direct object marker/particle, and it indicates what the verb acts on or is applied to. In this case, the verb is a polite imperative (ください = "give me") so を marks what is to be given, パン.
On the other hand, は is usually called the topic marker/particle. "Topic" is a bit strange for English-speakers because we don't explicitly have "topics" nor do we use the concept very frequently, it's essentially the anchoring point for the sentence and the context. Often it's useful to think about it as meaning "as for..." or "when it comes to...", though you should avoid including such phrases in your final translation.
For example: ジョンさんは先生です = "As for John (=ジョンさんは), [he] is (=です) a teacher (=先生)"
When は marks something as the topic, it often (but not always) overrides another particle, taking over its role and elevating the marked thing to the topic. In the earlier example, は replaced が which is the subject marker/particle, which indicates the agent that does the verb. In other cases, は can replace を as the object marker, often to emphasize a question, a negative, or a comparison.
は is a very versatile particle, but it isn't all powerful. You can't use it with ください because ください is a kind of auxiliary verb which needs to act on a direct object.