String classes rarely use UTF-16 because it doesn't have fixed length code point representation. UCS-2 is often used instead, which uses two bytes to represent

String classes rarely use UTF-16 because it doesn't have fixed length code point representation. UCS-2 is often used instead, which uses two bytes to represent all the unicode points in the Basic Multilingual Plane (BMP), which is enough for 99.99% of the use cases. One example of this is Python, which used UCS-2 until version 3.3. There was a compile time option to use UCS-4, but UCS-2 was enough for most cases because the BMP contains all the characters of all the languages currently in use.