Sorry, francois. I haven't seen this topic.
LXDE uses GTK as the base framework, and LXQt uses Qt, so I think we should avoid mixing these two frameworks (not exactly a rule, but more like a good practice). That being said, I still miss some good Qt-based stuff. For example:
4- NetworkManager Applet;
As for a simple text editor for Qt, I like FeatherPad. I know there are many others, but this is the only one that is both light and has no problems with encoding (you probably deal with French, so you understand how critical this is).
Leafpad although not Qt-based is also a good option, but recently it has some issue with drag 'n drop.
As for a audio player for Qt, I'm using Qmmp since I'm a Winamp fan (back from the good old 90's
), and I always like the idea of a simple and powerful app. It opens basically any audio format and has tons of possibilities with plugins.
As for a video player, Mpv is the best player so far, no doubt about it. However, its basic interface annoys some people, so many of them prefer to install a frontend, like Gnome Mpv (GTK) or SMPlayer (Qt). IMO, as long as you tweak Mpv configuration files, it's pretty usable: auto loading subtitles, setting basic shortcuts, showing video info in the screen, etc. So if it could depend on me, I wouldn't use any frontend for Mpv.