I18n: Update translation it (100%).

283 translated messages.

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

283 translated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
I18n: Update translation cs (99%).

281 translated messages, 2 untranslated messages.

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