Fontconfig supports modify charset during font scan since 2010. This is helpful if you want to limit matching on some fonts to a modified charset, rather than the actual charset in the font file.

I created the user configuration in the attachment to prefer Noto Sans CJK SC for sans-serif alias, only when the Unicode code point of the character is in the range of CJK code blocks, so that I can use Noto Sans CJK SC for CJK characters but Asana Math for non-CJK characters, such as Latin characters.

This works correctly in GTK applications as shown in attachment, but in Qt applications both CJK characters and non-CJK characters are using Noto Sans CJK SC. Both GTK application and Qt application in screenshot used Sans or sans-serif as application font.

From Qt source code:

https://code.woboq.org/qt5/qtbase/src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp.html#_ZNK19QFontconfigDatabase18fallbacksForFamilyERK7QStringN5QFont5StyleENS3_9StyleHintEN5QChar6ScriptE

It looks like Qt does not add FcCharSet to FcPattern when calling Fontconfig to find a preferred font family.