How to translate a warning message?
Depending on how often it appears, you can call t(SPAMBOT_DEFAULT_BLOCKED_MESSAGE) every time you invoke the constant in your code. For instance:

&lt;?php

define('SPAMBOT_DEFAULT_BLOCKED_MESSAGE', 'Your email address or username or IP address is blacklisted.');

/**
 * implement hook_page_alter()
 * JUST AN EXAMPLE. REPLACE WITH YOUR OWN HOOK OR FUNCTION
 */
function mymodule_page_alter(&amp;$page) {
  drupal_set_message(t(SPAMBOT_DEFAULT_BLOCKED_MESSAGE));
}


In order to be able to see the string in the "Translate interface" page (admin/config/regional/translate/translate), you need to display it at least once in a language different from the default language of your site.