I set up a custom GlyphData file to add new categories for my glyphs. My categories use some Han script characters.
These characters appear to render with G-region glyphs (for mainland China). I would expect J-region glyphs to match my settings in System Preferences > Language & Region > Preferred Languages, which are ➀ English, ➁ Japanese, ➂ Chinese (trad), and ➃ Chinese (simp).
This issue doesn’t create a real problem for me, but it could be problematic for other scripts.