Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Update korean locale messages:

- Remove redundant `s' and `S' from yesexpr.
- Add fullwidth latin letters to yesexpr and noexpr (inspired by ja_JP.UTF-8).
- Add korean translated yesexpr (`Ye') and noexpr (`Anio').
- Add yesstr and nostr entries (inspired by zh_CN.*).
- Add UTF-8 encoded file and connect to build.