When running misc/cronjobs/holds/holds_reminder.pl it looks like borrowers.lang is not respected. The only code I can see that relates to language is this:

    # FIXME What if we don't want to default if the translated template does not exist?
    my $template_exists = Koha::Notice::Templates->find_effective_template(
        {
            module     => 'reserves',
            code       => $lettercode,
            branchcode => $branchcode,
            lang       => 'default',
        }
    );

As far as I can see, the "default" template is always used?