[Gentoo Weekly News] The locales a user can choose from are built by the glibc. Usually all available locales starting from aa_DJ (Afar locale for Djibouti) over en_US (English locale for the USA) to zu_ZA.utf8 (Zulu locale for South Africa) will be installed. Unless you're working at the UN and administer a central server for all member states, it is difficult to conceive why you would need a system where all of these locales are installed. This week's tip was written with all those of you in mind who'd like to save 90 percent of the space occupied by locales in their system, by limiting the number of installed locales to the bare minimum.
Ever since sys-libs/glibc-2.3.4.20040619-r2 has been in Portage, a USE-flag called userlocales was provided to make sure only those locales mentioned in /etc/locales.build are to be built and installed. As a side-effect, this also leads to a much faster emerge of glibc, obviously.

