drupal_mail sending wrongly encoded special characters in mail subject
There are no bugs. Maybe lazy code from the developers.

Just simply put this line

mb_encode_mimeheader($params["subject"],"UTF-8", "B", "\n");

for the subject and works in all languages and codifications (chinese, etc.). It is tremendous that phpMailer class in itself handles perfectly, but when you use the phpMailer module, this encapsulating dissapears and you have to hard-code in the mymodule_mail() function.

Sincerely, Drupal is not suited for big projects.