When is it appropriate to use the original pronunciation of a foreign word versus the English pronunciation?

When reading to an audience, or speaking in conversation, when is it appropriate to use the original pronunciation of a foreign word versus the English pronunciation (assuming you know the appropriate pronunciation for it)? Is it considered rude, or condescending? Or is it considered a mark of being knowledgeable?

One of the things to consider are place names. When referring to Paris, France, should it be pronounced with the silent 'S' as the French would say it, or with the 'S'? Should Hiroshima be pronounced as a Japanese speaker would pronounce it slightly more emphasis on RO, rather than the SHI? Should Mount Pinatubo be pronounced as a Filipino speaker would pronounce it with shorter stronger vowels, or the longer vowels? (e.g. Pi as is 'pick' rather than 'pea'.) Should Wichita be pronounces as the original "shi" rather than the modern "chi"?

Pronounce pesos or sombrero as a Spanish speaker 'eh' or the English 'ay'?

(I can't think of other common words right now that aren't words taken from other languages like hurricane, boondocks, tornado, etc. which I think have (correctly) changed to English pronunciations.)

For words which are commonly used in English (like "Paris") using the foreign pronunciation is guaranteed to sound pretentious.

English has a distinctive phonetic pattern, and switching to another phonetic system in the middle of a sentence for the purpose of pronouncing a different place name would sound odd and draw attention to yourself. Imagine an American speaker switching to a British accent every time he had to say "England". When speaking in an American accent, saying frahns instead of fraens (for France) is unbearably pretentious... even though frahns is the way it's pronounced in British English.

For more rarely used words (for example, small place names rarely mentioned in English), using foreign pronunciations won't be noticed. Nobody in America has ever heard of Ramat Gan, Israel, so pronouncing it the Israeli way (raMAT GAN) instead of the English way (RAMat GAN) won't even be noticed... but with American audiences, switching to American phonetics is always appreciated (using a hard American R instead of a gutteral or fricative will help people understand what you said).

If I am talking to a native French person, it may show appreciation for his language and culture to use the French pronunciation. On the other hand, there may be cases where using the French pronunciation would feel condescending.

When speaking to an audience, I think it is appropriate to use whatever you think will be the most understood. If I am talking to a group of Americans who have very little or no knowledge of French, they may not understand if I used a foreign pronunciation.

Communication is about building relationships. If I alienate someone by using a particular pronunciation, I am defeating the purpose of our interaction. To consolidate my answer to one sentence: Pronounce in whatever way will build the most solidarity between yourself and those to whom you are communicating.

Paris is the English word for the French city "Paris", as Florence is the English word for the Italian city "Firenze". It is the translated place name and therefore should have the English pronunciation. That is my recommendation for translated words in general, even if the spelling is the same as in the original language.

But if the word is really not English, then I'd say the speaker should use the original pronunciation.

Personally, I always go with the English pronunciation, even when speaking to a knowledgeable audience. This is mainly for two reasons:

• The English pronunciation is more familiar, even to knowledgeable people. They simply hear it more often. They might know how karate is pronounced in Japanese, but hearing [kəˈrɑːtiː] still makes them feel better, if only subconsciously. English and Japanese are stored in two entirely different parts of their brain, and while some people can constantly flip switches in their brain in the middle of a sentence, nobody really wants it. It is always an effort, however minor.
• More importantly though, I just don't see any need to use the original pronunciation. When I'm speaking English, I'm speaking English. If I wanted to speak French instead, I'd be speaking French. The English pronunciation of Paris is not incorrect in any way or by any measure. Yes, it's different from the French one, but so what?

If we started pronouncing everything the same in all languages, languages as we know them would cease to exist. I don't want to live in that world.