[wvenable]

Windows and many other operating systems and languages (Java) got on board with Unicode back when the character set would fit in 16bits. The character set originally used was UCS-2 (not UTF-16). UTF-16 came next to extend the Unicode character set beyond 65536 code points.

UTF-8 wasn't even invented until well after all these operating systems and languages deployed Unicode.

They didn't see the light of day to use UTF-8 because they didn't have a time machine to make that possible.

[flohofwoe]

I actually checked a while ago when UTF-8 was created, and it was just around the same time when Windows NT was developed with 16-bit "early" Unicode support. UTF-8 was created in September 1992 [1], and Windows NT came out mid 1993, but I guess it was too late for Windows to change to UTF-8 (and I guess the advantages of UTF-8 haven't been as clear back then).

But IMHO there's no excuse to not use UTF-8 after around 1995 ;)

[1] https://www.cl.cam.ac.uk/~mgk25/ucs/utf-8-history.txt

[gpvos]

Also, UTF-16 was only published in July 1996 (although the need for more than 16 bits was probably apparent a bit earlier). So before that, Unicode was only a 16-bit encoding, and UCS-2 was enough. UTF-8 was initially just a nice trick to keep using ASCII characters for things like directory separators (/) and single-byte NUL terminators. By 1995 its superiority certainly wasn't apparent yet.

Also, Windows internals were completely 16-bit-character based, including e.g. the NTFS disk format, so by 1992 that was already quite hard to change.

That said, it is crazy that NT didn't have full UTF-8 support, including in console windows, by about 2000.