This is dev-texlive/texlive-basic-2012's DEPEND: DEPEND=">=dev-texlive/texlive-basic-2012 >=app-text/texlive-core-2010[cjk] >=dev-texlive/texlive-latex-2011 !!<dev-texlive/texlive-langcjk-2012 " I guess the double negation is a typo. Now =dev-texlive/texlive-langcjk-2012 depends on !!<dev-texlive/texlive-langcjk-2012, that is, <dev-texlive/texlive-langcjk-2012 and therefore can't be installed. Reproducible: Always
Sorry, it's dev-texlive/texlive-langcjk-2012, not dev-texlive/texlive-basic-2012. I fixed the bug title, but the first line in the bug description is still incorrect (it should say "dev-texlive/texlive-langcjk-2012" instead).
In ebuilds, !! is a more rigorous version of !. See man 5 ebuild. Just run "emerge -C texlive-langcjk" before updating world.
Right, sorry. I'm closing this as invalid then.