When i want to change the background in Archlinux, there's no option to add more wallpaper or picture into Deepin Desktop Environment. But i found a app that can help to change background in Deepin Desktop environment. It is Wally, wally is a desktop background / wallpaper changer for QT4.
The source code is here:
https://sourceforge.net/projects/wally/
In archlinux, it's available on AUR:
https://aur.archlinux.org/packages/wally/
There's no menu for wally, so run at command line:
$wally
Then it will appear on panel, right click on wally, then go to settings:
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Then choose folder, and add your background/wallpaper folder, set the position then ok:
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Right click again on Wally menu then choose play, and just next to choose the wallpaper, here's the results :
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it will be also appear on your Deepin wallpaper list