In Spanish, it is not unusual to retain the original titles, if only to remark the nationality of the person to whom they apply. You can also find references to Frau Merkel or Monsieur Hollande, even in original (not translated) texts. I am not saying that this is extremely usual, but it is not unusual. At least, for English, French or German titles.
Besides, in this case we would not use the article. So, we could write Las propuestas de la señora Merkel, but Las propuestas de Frau Merkel. The latter construction remarks the fact that she is German.