http://www.gentoo.org/doc/en/guide-localization.xml#doc_chap6 still refers to kde-base/kde-i18n KDE3 package. It would be better to add some info about the equivalent KDE4 package kde-base/kde-l10n too.
I close this bug by myself, nightmorph have already fixed the document: http://sources.gentoo.org/viewcvs.py/gentoo/xml/htdocs/doc/en/guide-localization.xml?r1=1.58&r2=1.60