I18n: Update translation ar (100%).

44 translated messages.

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

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

44 translated messages.

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