To get thousands separators in file sizes, I added values (0x2C) for thousand_sep and thousep in /etc/login.conf, and called cap_mkdb to update the db.
Inspection of /etc/login.conf.db showed that those vars were now defined.
But when I logged in again and called locale -k, the values were again/still the empty string.
Even saving a copy of login.conf as ~/.login.conf, per the docs, and cap_mkdb'ing there, too, made no difference.
Apparently there's some locale data hardcoded somewhere that's being used, while the config files and their databases are being ignored.
Where is it documented that keywords in login.conf override the locale data? I can't find anything related in the code and/or documentation.