I'm not sure if this was being somewhat disingenuous, because I know you're well aware of the particular focus on Unicode-correctness for strings in Swift, but I'll take it at face value. It would be great if you would follow up on the category of “Code unit/code point/Unicode scalar” by specifying what the default “atom” of a string is in these languages, e.g. something like what you get when you index into a string, or what the string's length is calculated in terms of. A quick skim and spot check of a couple of them didn't reveal anything similar to Swift in this respect. Languages which are less interested in Unicode-correct strings are of course going to have a different idea of what this “atom” or “character” is, and that is generally reflected in their “character” syntax, so I don't find this survey very relevant here.
Edit: And of course, this delusion about the obvious default type for single quoted literals isn't unique to me and @RMJay: