Due to Han unification and other similar stuff parts of some fonts may not be suitable for all locales.
This is handled by the locl flag in modern opentype fonts.
However there are still many non-opentype fonts in the wild, and it is not possible to convert them all at once (when the license permits it).
There should be a way in fontconfig for font distributors to patch in via a config file the locl characteristics of a font.
Make "a way" a "documented fonts.conf config pattern".
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