I18n: Update translation da (93%).

70 translated messages, 5 untranslated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
I18n: Add new translation sl (53%).

40 translated messages, 35 untranslated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).