Hi Thierry,
I didn't know that the Q4OS Team used a non standard TDE, in fact they straight out
told me it's a TDE issue, as you can read from my post in their forum, of which I left
the URL.
As for the applications which display the issue, Dolphin and VLC are the most notable
ones, Firefox does not have this issue, for example.
I installed noto-fonts because many solutions that came up googling around suggested to do
so.
Thanks