SpamAssassin can detect certain languages and character sets. Both language and character set information are added by email clients when emails are composed and sent, so that the receiving email client can display the message correctly. There are many languages and character sets in use. If received messages are expected or known to use only some of them, then the others can be filtered out.
SpamAssassin detects languages by using email headers. There is a large list of languages that SpamAssassin can detect; these are listed in the documentation for
Mail::SpamAssassin::Conf. Use the
perldoc commands to view the documentation:
$ perldoc Mail::SpamAssassin::Conf $ man Mail::SpamAssassin::Conf ...