I realized that on the servers where the Load Average monitor did not work, there was the file "/etc/default/locale" with the next content: # File generated by update-locale LANG=es_ES.UTF-8 On servers where this file did not exist, or was empty, the Load Average Monitor from Webmin works correctly. Except in an old Debian 6, which works even if it exists and has that variable set to LANG=es_ES.UTF-8 However, it would be convenient that this works even if this file exists and is setting some value....
load average monitor doen't work on server using locale LANG=es_ES.UTF-8