Change locale (LC_NUMERIC) in appropriate places so we always use the
user's locale when reading/writting floats to config (otherwise it would
read floats using C locale (float separator is . in C) and write them
using the user's local (float separator can be , instead of .))

If these changes aren't ok, then i think that the only solution would be
to always setlocale(LC_NUMERIC, "C") when handling config str<->float
conversions.