set separate-locales to force archive to use user's system language

I added lines 7 and 8 to force the flatpak archive to use the user's system language. It worked on my testing VM.

org.gramps_project.Gramps.yml

@@ -4,6 +4,8 @@ runtime: org.gnome.Platform
 runtime-version: '44'
 sdk: org.gnome.Sdk
 command: gramps
+# to force an archive flatpak to use system locale instead of English. Not needed for flathub packages.
+separate-locales: false
 rename-icon: gramps
 rename-desktop-file: gramps.desktop
 finish-args: