t() and format_plural() let you provide little bits of additional information to specify the context for shorter strings, so translators know how to translate ambiguous text.
This feature is now extended to their Javascript counterparts Drupal.t() and Drupal.formatPlural().
Example:
You can retrieve the long month name translation of May (as opposed to the short version) with:
Drupal.t('May', {}, {context: "Long month name"});
