(set-language-environment): Use

(set-language-environment): Use
functionp, not fboundp.
(locale-language-names): Don't special-case utf-8.  Use
Cyrillic-iso in place of Latin-5 for Cyrillic locales.
(locale-charset-language-names, locale-preferred-coding-systems):
Add utf-8.
(sort-coding-systems): Use coding-priority property, not
coding-system.