TLDR - this is a Flatpak mixed locales issue. flatpak config --set languages 'en;sr' (I mix Serbian and English) and then flatpak update handles it, Orion should run after other language is set.
Alright, this is a Flatpak issue, not directly an Orion problem. I managed to run it by enforcing the LC_ALL locale with sudo flatpak override --env=LC_ALL=en_US.UTF-8 com.kagi.OrionGtk, but that's just for making it run, I need to figure which locale is messing it up actually.
Update
Tried setting non English locales I have on my system manually, looks like LC_MEASUREMENT is making a mess:
> sudo flatpak override --env=LC_MEASUREMENT=sr_RS.UTF-8 com.kagi.OrionGtk
> flatpak run com.kagi.OrionGtk
13:56:35.946347[I] orion-linux is starting
(process:2): Gtk-WARNING **: 13:56:35.950: Locale not supported by C library.
Using the fallback 'C' locale.
flatpak-spawn: Invalid byte sequence in conversion input
Try "flatpak-spawn --help" for more information.
** (process:2): ERROR **: 13:56:51.188: readPIDFromPeer: Unexpected short read from PID socket
> sudo flatpak override --env=LC_MEASUREMENT=en_US.UTF-8 com.kagi.OrionGtk
> flatpak run com.kagi.OrionGtk
13:57:11.119874[I] orion-linux is starting
Serbian UTF-8 is not working, but it runs fine with English US.
Update 2
I think I got to the bottom of this. Flatpak seems not to be capable of handling mixed locales properly, there's even a bug report for that issue. Anyway, other flatpaks were reporting the same locales issue which flatpak config --set languages 'en;sr' (I mix Serbian and English) and then flatpak update fixed. However, other apps do not crash because of that, so I guess Orion Linux devs should apply whatever is needed for app not to crash when Flatpak can't handle mixed locales.
