Non-English characters, special characters, &#dddd; and &#xhhhh;
Besides open/edit/save in proper utf-8 or other Unicode charset encoding, the editor really needs to be able to change chars in a selection or a whole file back and forth from the actual char to the &#xhhhh; entity or the named entity, such as þ or é or ’ .
Why? Because whether you use only English, with proper typography, or you need one or more additional languages, you will always want to enter and view the text easily in native characters, or transform it into them if the file does not have them. If a program (erroneously) alters special characters into a ? or other char, it is very hard or unusable. (I have seen other programs make that mistake.)
Suppose you need to have English, plus a Latin alphabet with many accent marks (almost any European language), or Greek, or Russian (Cyrillic alphabet)... Or even more exotic, like any Asian or Indian or Middle Eastern script. Or suppose you need some really exotic thing from some obscure language or historical source available in Unicode.
Chances are, you require that in the native text characters. Chances are pretty good you also have to put that into &#xhhhh; or &named; entities at some point for display and compatibility. That assumes, of course, a &named; entity even exists. (There is none for schwa e lowercase or uppercase, or macron or breve vowel accents, for example.) And no one sane would suggest attempting to wade through a bunch of ampersand-pound-numerical-string-semicolon runs for, say, Japanese, or a paper on early writing systems.
That's why people are asking about foreign language characters. They need to see them natively *and* they need to transform on demand into the &-sign entities. Seeing a bunch of question marks instead of readable native language text, either in code view or browser preview is not helpful. Not if you are a native speaker who expects to see his/her own language, and not if you are a translator/linguist who expects the same, and not if you are someone trying to communicate and function with people, even if they don't happen to speak (American) English only. Go to any grocery store or mall in a major US city, and you will find US citizens, immigrants, and guest visitors or workers who speak, write, and think in another language (or many) besides English. Or, for that matter, Native American Indian folks use a few things other than English (Cherokee, for one). These are not just people in some foreign country. They are right here, and our friends, relatives, and trading partners.
The ability to transform a text selection or a whole file, back and forth, is really needed. How many registered users, and their contacts, use languages besides English? Nearly all of them, once you get to friend or friend of a friend especially.
It could come in handy for the next scholarly paper or the next historical or science fiction novel or video.