> Internally, the model of a String is UTF-16-like, a sequence of unsigned 16-bit `char` values.

That is not 100% true anymore. Java 9 (September 2017) changed “the internal representation of the String class from a UTF-16 char array to a byte array plus an encoding-flag field. The new String class will store characters encoded either as ISO-8859-1/Latin-1 (one byte per character), or as UTF-16 (two bytes per character), based upon the contents of the string. The encoding flag will indicate which encoding is used.” (https://openjdk.org/jeps/254)