help: fix search with `-k` option in non-ASCII locales
Keyword search in help (introduced in 497deec204d1 and a17983680f12 by Augie
Fackler) tries to translate already translated strings, which results in
Unicode errors in gettext when non-ASCII locale is used. Also command
descriptions should be translated before searching there (thanks to FUJIWARA
Katsunori for pointing this out and actual fix), (issue3482).