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