see https://github.com/postfixadmin/postfixadmin/issues/236

languages/en.lang

@@ -414,6 +414,7 @@ $PALANG['pFetchmail_desc_returned_text']    = 'Text message from last polling';
 $PALANG['dateformat_pgsql'] = 'YYYY-mm-dd'; # translators: rearrange to your local date format, but make sure it's a valid PostgreSQL date format
 $PALANG['dateformat_mysql'] = '%Y-%m-%d';   # translators: rearrange to your local date format, but make sure it's a valid MySQL date format
 $PALANG['password_expiration'] = 'Pass expires';
+$PALANG['password_expiration_desc'] = 'Date when password will expire';
 
 $PALANG['please_keep_this_as_last_entry'] = ''; # needed for language-check.sh
 /* vim: set expandtab ft=php softtabstop=3 tabstop=3 shiftwidth=3: */