How is the character represented in Swift strings?

let flag = "\u{1f1e9}\u{1f1ea}"

then flag is 🇩🇪 .

For more regional indicator symbols, see:
http://en.wikipedia.org/wiki/Regional_Indicator_Symbol

Support for "extended grapheme clusters" has been added to Swift in the meantime. Iterating over the characters of a string produces a single character for the "flags":

let string = "Hi🇩🇪!"
for char in string.characters {
    print(char)
}

Output:

H
i
🇩🇪
!