Multiple xeCJK fonts

Question

I have set my main font for xeCJK to HanWangMingMedium, so that I can access old style characters. But, as a result, I no longer have access to Japanese kana: in the MWE, the katakana comes up as white space:

The default xeCJK font doesn’t create this problem, but doesn’t give me certain characters that I need (like 烝). How do I change xeCJK fonts within the body of the document, and what is the default xeCJK font called?

Possibly relevant to an answer: I’m writing about writing systems. So, I only need isolated characters. I don’t have long sections of Chinese text.

% !TEX encoding = UTF-8 Unicode
\documentclass{article}
\usepackage{fontspec}
\usepackage{xeCJK}
   \setCJKmainfont{HanWangMingMedium}
\begin{document}

東風フォント

\end{document}

---

Update. Here's a hack: pretend the alternative font is the sans serif variant. But I'd still like a proper solution.

% !TEX encoding = UTF-8 Unicode
\documentclass{article}
\usepackage{fontspec}
\usepackage{xeCJK}
   \setCJKmainfont{HanWangMingMedium}
   \setCJKsansfont{AozoraMinchoRegular}

\begin{document}

東風\sf フォント.

\end{document}

Answer 1

In babel, you can switch between different ideographic alphabets, including Japanese and traditional Chinese:

\documentclass{standalone} % Replace with the real class.
\usepackage[english]{babel}
\usepackage{fontspec}

% A bug in Babel 3.22 requires setting the script= option to CJK and Kana,
% respectively.
\babelprovide{chinese-traditional}
\babelprovide{japanese}

\defaultfontfeatures{Scale = MatchUppercase}
\babelfont{rm}[Scale = 1.0,
               Ligatures = {Common, TeX},
               Language = Default
              ]{Latin Modern Roman}
\babelfont{sf}[Ligatures = {Common, TeX},
               Language = Default]{Latin Modern Sans}
\babelfont[chinese-traditional]{rm}{NotoSerifCJKtc-Regular}
\babelfont[chinese-traditional]{sf}{NotoSansCJKtc-Regular}
\babelfont[japanese]{rm}{NotoSerifCJKjp-Regular}
\babelfont[japanese]{sf}{NotoSansCJKjp-Regular}

\begin{document}

\otherlanguage{chinese-traditional}{東風}
\otherlanguage{japanese}{フォント}

\end{document}

This requires XeLaTeX and babel 3.27 or higher. (With babel 3.22, you must manually set Script=CJK and Script=Kana to work around a bug.) I substituted the Noto CJK fonts.

A simpler option to Babel that doesn’t require you to write \otherlanguage all over the place would be ucharclasses. You could also declare a \newfontfamily, give it the [Script = Kana, Language = Japanese] options, and select that.

Update

As of 2021, it’s possible to use multiple ideographic scripts in LuaLaTeX 1.12 or later. In theory, you can set your document up to switch between the languages without tagging. In practice, this does not reliably work for Chinese and Japanese, because the Unicode Consortium chose to use the same codepoints for Kanji and Chinese. (The original sin of Unicode was thinking they could fit everything into 16 bits.)

In this specific example, if the only Japanese we need is Hirigana and Katakana, and all ideographic characters are Chinese, we can make babel detect Japanese, Chinese and English correctly:

\documentclass{standalone} % Replace with the real class.
\usepackage[english]{babel}
\usepackage[svgnames, HTML]{xcolor}
\usepackage{fontspec}

% A bug in Babel 3.22 requires setting the script= option to CJK and Kana,
% respectively.
\babelprovide[import, onchar=ids fonts]{japanese}
\babelprovide[import, onchar=ids fonts]{chinese-traditional}

\defaultfontfeatures{ Scale = MatchUppercase,
                      Ligatures=TeX }
\babelfont{rm}
          [Scale = 1.0,
           Ligatures = Common,
           Language = Default
          ]{Latin Modern Roman}
\babelfont{sf}
          [Ligatures = Common,
           Language = Default
          ]{Latin Modern Sans}
\babelfont[chinese-traditional]{rm}
          [Renderer=HarfBuzz, Color=DarkGreen]{NotoSerifCJKtc-Regular}
\babelfont[chinese-traditional]{sf}
          [Renderer=HarfBuzz, Color=DarkGreen]{NotoSansCJKtc-Regular}
\babelfont[japanese]{rm}
          [Renderer=HarfBuzz, Color=NavyBlue]{NotoSerifCJKjp-Regular}
\babelfont[japanese]{sf}
          [Renderer=HarfBuzz, Color=NavyBlue]{NotoSansCJKjp-Regular}

\begin{document}

東風
\textsf{フォント}

\end{document}

Here, I set each language to a different color to make the language-switching more obvious.