mplayerplug-in contains a lot of translations but they are not installed in Gentoo because offical "make install" doesn't install them automatically.
Created attachment 123255 [details, diff] net-www/mplayerplug-in-3.40-r2 Adds NLS and linguas_* use flags. Their propper combination results in gettext catalogs installation.
Thanks! I've added this to mplayerplug-in 3.45.