"UCS-2 (2-byte Universal Character Set) is a character encoding that was superseded by UTF-16 in version 2.0 of the Unicode standard in July 1996". Java adopted UCS-2 which was later supplemented with UTF-16 support.

There are at least a few languages in this world which do not use roman letters and are better represented as multibyte sequences :). That is why Java added support for supplementary UTF-16 characters over and above UCS-2. That said, use of UTF-8 would have been optimal for western languages, but sub optimal for several other languages.

Wrong. UTF-16 is an encoding, Unicode is the abstract representation. You can encode Unicode strings into UTF-16, but that doesn't make UTF-16 Unicode. Python's Unicode strings are actually really just Unicode, that's why you can't write them to a file or anything - you need to encode them first (which defaults to UTF-8).

In Java, you end up seeing the guts of UTF-16 far more often than you should. Most notably, the String APIs often index strings by UTF-16 code units, not characters, so string "lengths" don't always correspond to the number of Unicode characters, and you can end up cutting surrogate pairs in half if you aren't careful.