Native US speaker - the answers may be different for UK speakers 1 - Badly. Probably "bool deh sweef" with an inflection to let everyone know that I have no idea how to say the words. 2 & 3 - To be clear, we also mispronounce "Maupassant." We will definitely mispronounce the title of his works. (In English, the story is known as "Dumpling" - we don't even try.) No, we're not taught french pronunciation in school. Many Americans never learned any foreign language. Some took one language for a year in high school. We tend to be monolingual. When we see a name or phrase that is obviously non-English, we will sound it out as best we can, substituting in random rules that we vaguely remember from past encounters with other languages. So, when encountering a word that looks like it might be Spanish, many speakers will start rolling their "r"s, pronouncing "j"s as "h," and throw in an "ñ" even when the letter is clearly "n." French seems to have a lot of silent "s"s, so we just stop pronouncing them altogether in French words. (Every year, we can't seem to figure out how to pronounce "Cannes" during the film festival. During news reports, each broadcaster will say it differently) We still have limited contact with non-Anglicized Chinese words, but I'm willing to bet we'll do horrible things to the tones. In the meantime, people will probably use the rules of the language they studied for one year in high school.

Hello Hy. I'll answer your questions a bit out of order.

1) As a native speaker of English from the Southern United States, I would say "bool-de-sweef".

3) English has a long history of borrowing foreign names phrases, so usually when one encounters something in written form, the spelling has been anglicized sufficiently that, even without knowing the language of origin, the reader can sound it out and pronounce it well enough to be understood. One just has to learn the phonetic rules for the region that he wants to emulate (for example, Midwestern American dialect for standard American English, or the Queen's English for standard British English)

2) The way a native English speaker would pronounce a foreign name or phrase depends largely upon where they are from, with differences between British and American English, and even further variations from region to region. For example, there is a town here in Texas called Palestine. Since it is spelled the same as that place in the Middle East, one might expect it to be pronounced 'Pal-is-tyne', but native Texans say 'Pal-is-teen'.

I may be able to answer your third question. Based on my experience, sometimes those words have been in the vocabulary (loan words) like dim sum, bun, pho and most French and Italian dishes. For other unfamiliar cuisines, English speakers may make a guess based on the spell, for example bimbimbap, gyudon, yakitori, etc. But for some foodies, they know those words as well.