Man pages matching name mfontset_modify_entry in section 3m17n:

mfontset_modify_entry.3m17n.en	debian 10 / m17n-docs
mfontset_modify_entry.3m17n.en	debian 11 / m17n-docs
mfontset_modify_entry.3m17n.en	debian 12 / m17n-docs