http://www.youtube.com/watch?v=dP3ZH0vbueU *
The title is the question: why are the Spanish names used for NYC and New Orleans (“Nueva York” and “Nueva Orleans”), but not for Kansas City and Buffalo? (“Cuidad Kansas” and “Bufalo”)?
Why do I feel hot all of a sudden? 
Significant Spanish-speaking local population?
Another possibility is that NYC & NO register on the international scene in ways that KC & Buffalo do not, so Spanish-speakers abroad have a word for some U.S. cities and not others. Much the way we speak of Florence and Naples rather than Firenze and Napoli, but have no problem discussing Piacenza and San Gimignano in Italian. (Sorry, I couldn’t think of any Spanish examples.)
And no doubt irrelevant, but as far as I know the only U.S. city the Welsh discuss in Welsh is Efrog Newydd, even when there’s an obvious translation (Los Angeles = Yr Angylion; St. Petersburg = Llanpedr / Lampeter).
Assuming you meant Spanish language as opposed to geographically Spanish, how about Mexico City vs Ciudad Juarez (sometimes just Juarez, but never Juarez City)?
I’ve never heard anything called Ciudad in English.
I can’t think of any other cities off the top of my head with Cuidad in the English name, but it seems pretty common for Ciudad Juarez. Cite: ciudad juarez - Google Search
What they said. There is a varying, hard-to-pin-down convention among various Western languages that links the practice of translating and/or transposing to your own phonetics the name for a place or person, with how and when the name entered the consciousness of the majority of a language’s speakers. Similarly, in Spanish it’s Jorge Washington, but George Bush; it’s “Londres” for London but Liverpool is what it is. “Nueva” Orleans of course has the particularity that from 1769 to 1802 that WAS the official name, while you bet anglophones and francophones were still calling it “New” and “Nouvelle” on their maps just the same.
And I very much want want her to tell me about the effects of mountains on climate patterns in deep valleys, Og help me…
Which is???
There’s actually some logic to that. The actual name of Mexico City is “Mexico.” “City”/“Ciudad” is not part of the formal name, but just appended to distinguish it from the country. So it’s not “Ciudad Mexico,” but “Ciudad de Mexico.” The same goes for Guatemala City and Panama City; their names are simply “Guatemala” and “Panama” respectively. (Panama City, Florida, however, actually is called “Panama City.”)
Ciudad Juarez is different, in that “Ciudad” is actually part of the name. It is sometimes called Juarez for short; however, it is never called “Ciudad de Juarez,” indicating that Juarez alone is not the city’s name.
The same thing applies to city names in English. The formal name of New York City is “New York”; it can also be referred to as “The City of New York.” This is not the case for Kansas City or Jersey City, where “City” is a integral part of the name. You would not refer to them as “The City of Kansas” or “The City of Jersey.”
Ciudad Juarez is by far the best-known one, but there are also Ciudad Obregon and Ciudad Victoria in Mexico, and Ciudad Bolivar and Ciudad Guayana in Venezuela; there are others. Santo Domingo in the Dominican Republic was formerly known as Ciudad Trujillo.
Sorry. Efrog = York (both from Eboracum) and Newydd = New, in other words New York.