Locales - dpopchev/howto-quick-setup-gentoo GitHub Wiki

See supported locales

less  /usr/share/i18n/SUPPORTED

Add target locales

grep -iP 'en_US|bg_BG' /usr/share/i18n/SUPPORTED >> /etc/locale.gen

Generate

locale-gen

Select

eselect locale list
eselect locale set ${YOUR_CHOICE}
env-update
source /etc/profile
export PS1="(chroot) ${PS1}

Use L10N in to specify extra localization support, commonly used for downloads of additional language packs by packages. Gentoo wiki