I can confirm that this is the case. It outputs the following warning/error message when you attempt to type an accented character:
qt.xkb.compose: failed to create compose table
It attempts to read the following paths, so we possibly have an incomplete locale location override in the KDE framework snap:
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.dir", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.dir", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.dir", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/locale.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/home/dllewellyn/snap/okular/90/.XCompose", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 925444] openat(AT_FDCWD, "/usr/share/X11/locale/compose.dir", O_RDONLY) = -1 ENOENT (No such file or directory)