It was possible to install both packets at the same time, when you install kde-i10n with the USE-flag minimal. This flag was removed from the ebuild. [ebuild R #] kde-apps/kde-l10n-15.04.1:5::kde [15.04.1:4/15.04::kde] USE="handbook -debug% (-aqua%) (-minimal%*)" LINGUAS="de -ar -bg -bs -ca -ca@valencia -cs -da -el -en_GB -eo -es -et -eu -fa -fi -fr -ga -gl -he -hi -hr -hu -ia -id -is -it -ja -kk -km -ko -lt -lv -mr -nb -nds -nl -nn -pa -pl -pt -pt_BR -ro -ru -sk -sl -sr -sv -tr -ug -uk -wa -zh_CN -zh_TW" 0 KiB And now it blocks kde4-l10n. [blocks B ] kde-apps/kde4-l10n[-minimal] ("kde-apps/kde4-l10n[-minimal]" is blocking kde-plasma/baloo-5.9.0, kde-plasma/kwin-5.3.0, kde-plasma/systemsettings-5.3.0, kde-plasma/kde-cli-tools-5.3.0, kde-plasma/kscreen-5.3.0, kde-plasma/libkscreen-5.3.0, kde-plasma/ksysguard-5.3.0, kde-plasma/kde-gtk-config-5.3.0, kde-plasma/sddm-kcm-5.3.0, kde-plasma/libksysguard-5.3.0, kde-plasma/khotkeys-5.3.0, kde-plasma/kmenuedit-5.3.0, kde-plasma/polkit-kde-agent-5.3.0, kde-plasma/kwayland-5.3.0, kde-plasma/kio-extras-5.3.0, kde-plasma/plasma-workspace-5.3.0-r1, kde-plasma/kwrited-5.3.0, kde-plasma/kdecoration-5.3.0, kde-plasma/milou-5.3.0, kde-plasma/plasma-nm-5.3.0, kde-plasma/kfilemetadata-5.9.0, kde-plasma/khelpcenter-5.3.0, kde-plasma/breeze-5.3.0, kde-plasma/kinfocenter-5.3.0, kde-plasma/ksshaskpass-5.3.0, kde-plasma/plasma-desktop-5.3.0, kde-plasma/oxygen-5.3.0, kde-plasma/powerdevil-5.3.0)
kde-apps/kde-l10n now only contains :5 translations kde-apps/kde4-l10n contains :4 translations, and there you need to set the minimal flag
Ok, in former days I set the minimal flag for kde-apps/kde-l10n, now I had to set it for kde-apps/kde4-l10n. Thank you very much.
This is now handled in the plasma profile.