Actually, don't have any idea how these icons were broken. Just after restarting my pc I found all these broken icons. Anyone know how to solve this issue [not a critical problem I must say, just bugging me] and thanks in advance.
It looks like a broken icon set. This could be caused by a wrong translation / language pack and / or changed theme.
You can try to set the Language and Region back to default (English) or try to reinstall the desktop.
Unfortunately I do not have a elementary OS running right now, but I think it can be done with
sudo apt-get install elementary-desktop