TODOs for Full UTF-8 Support https://wiki.freebsd.org/Unicode/TODO
ここのUseful Links (Ingo Schwarze's presentation on OpenBSD's use of UTF-8)でWhy and how you ought to
Keep multibyte character support simple (2016 Sep 25)が紹介されてる https://www.openbsd.org/papers/eurobsdcon2016-utf8.pdf
The OpenBSD way
We made a drastic decision!
The OpenBSD base system supports exactly two LC_CTYPE locales:
1. UTF-8
2. C = POSIX = US-ASCII
We don't even support ISO-LATIN-1 any longer in the base system.
https://www.openbsd.org/papers/eurobsdcon2016-utf8.pdf
…なるほど、mbstowcs()がlocaleの設定抜きでも動いちゃう(Linuxはlocaleの設定をしないと動かない)というのはこれが理由なのか。wchar_t使うようなものはUTF-8関連に決まっとる、と。