I18n: Update translation sv (100%).

283 translated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
I18n: Add new translation sl (50%).

142 translated messages, 141 untranslated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
I18n: Update translation fi (100%).

283 translated messages.

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