At the moment, XeTeX seems to be more stable and reliable for multilingual typesetting.
(When the version of LuaTeX bumps 1.0, this situation would change...)
here is a sample preamble code of CJK simultaneous typesetting (not tested yet)
\usepackage{zxjatype}
\usepackage[ipaex]{zxjafont}%日本語フォントを設定（メインとして）
\setmainfont{Gentium Plus}% 欧文フォントを設定
\usepackage{polyglossia}
\setotherlanguages{korean}%局所的韓国語環境
\newfontfamily\koreanfont[Script=Hangul]{UnBatang}%韓国語フォントを設定
\setjafamilyfont{chinesefam}{AR PL SungtiL GB} % 中国語フォント
% \chinese 命令: 中国語用の設定に切り替える。（局所的に使うべき）
\newcommand*{\chinese}{%
\CJKfamily{chinesefam}%
\punctstyle{fullwidth}%
\zxuseoriginalparameters}
% chinesepar 環境: 中国語用の段落の設定
% \chinese 設定に段落下げ量の変更（2zw）を含める
\newenvironment{chinesepar}%
{\par \chinese \setlength{\parindent}{2\jsZw}}{\par}
%
At the moment, XeTeX seems to be more stable and reliable for multilingual typesetting.
(When the version of LuaTeX bumps 1.0, this situation would change...)
here is a sample preamble code of CJK simultaneous typesetting (not tested yet)