Good morning
I'm a noob and i have a big problem that i have no idea how resolve it : I recently installed arch, and kde and when im on firefox and i want to upload a file this appear:
image of problem : https://postimg.cc/grvKfdDk
Help pls
Thankss

That is a localization problem. Different countries use different methods of displaying characters, most are completely incompatible.

What you are seeing is an attempt to render characters that the program doesn't know how to interpret. Since you are using Firefox, I'd say that's a Firefox issue. I don't know if KDE integration would help, but in any case you are most likely missing a package. Try asking in the Arch forums.

EDIT: Going out on a limb here, but it could also be your theme causing the issue.