One way you may choose to manage the mail that comes to the Postfix server is to use the locales which is a part of Spamassassin.  If you cannot read other languages there is really no need to run them through your mail system.  So for example if you wanted to limit email to English you would edit the:

/etc/mail/spamassassin/local.cf

ok_locales             en

This will treat any mail in character sets other than Western as spam. Here are the option that you have:

en   – Western character sets in general
ja   – Japanese character sets
ko   – Korean character sets
ru   – Cyrillic character sets
th   – Thai character sets
zh   – Chinese (both simplified and traditional) character sets
all  – Allow all character sets

This is an easy setting to help clean up mail that you cannot read anyway.