Trying to make japanese characters appear in the title of a section

Question

I have the following in my TeX:

\subsection{Buch 1 問題の日本語}

In my Table of Contents it is correctly displayed but in the subsection itself you can only see 1.1 Buch 1. I guess this is because the subsection title is bold in the main text and the Table of Contents text is not.

Some kind of solution to this to force the 問題の日本語 part not to be bold?

Minimal working example: (use XeLatex)

\documentclass[12pt]{scrartcl}

\usepackage{xltxtra} 
\usepackage[ngerman]{babel}
\usepackage{setspace}
\onehalfspacing
\setmainfont[ItalicFont=Arial Kursiv]{Arial Unicode MS} 

\begin{document}
\tableofcontents

\section{bla}
\subsection{Buch 1 問題の日本語}

\end{document}

Answer 1

The problem is not the bold font. scrartcl uses the sans family to print the subsection title. This is latin modern sans in your document. Either set the sans family to Arial too:

 \setsansfont[ItalicFont=Arial Kursiv]{Arial Unicode MS} 

Or switch to the main font before the japanese:

  \subsection{Buch 1\rmfamily 問題の日本語}    

(untested due to lack of time)

Answer 2

\documentclass[12pt]{scrartcl}

\usepackage{fontspec} 
\usepackage[ngerman]{babel}
\usepackage{setspace}
\onehalfspacing
\setmainfont[ItalicFont=Arial Italic]{Arial Unicode MS} 

\begin{document}
\tableofcontents

\section{bla}
\subsection{Buch 1 \textnormal{問題の日本語}}

\end{document}