dead-keys don't work after big upgrades (kde5)

After the big upgrades, dead-keys dead_circumflex and
dead_diaeresis are really dead with my french keyboard
azerty 105 keys.

Context :
- kernel 5.4.53 64bits
- non UTF-8 (boot parameter vt.default_utf8=0)
- LANG=fr_FR@euro
I have also tried fr_Fr, fr_FR.iso8859-15
- keyboard azerty 105 keys,
- setxkbmap -print :
xkb_keymap {
xkb_keycodes { include "evdev+aliases(azerty)"};
xkb_types { include "complete"};
xkb_compat { include "complete"};
xkb_symbols { include "pc+fr(latin9)+inet(evdev)+capslock(none)+eurosign(e)+terminate(ctrl_alt_bksp)"};
xkb_geometry { include "pc(pc105)"};
};
Note: I have tried all french variants without success
- depcheck is ok
- all installed slackware packages are in the tabfiles (no old packages installed)

When I startx, I get 10 errors :
kwin_xkbcommon: XKB: /usr/share/X11/locale/iso8859-15/Compose:38:34: string literal is not a valid UTF-8 string
kwin_xkbcommon: XKB: /usr/share/X11/locale/iso8859-15/Compose:39:29: string literal is not a valid UTF-8 string
...
kwin_xkbcommon: XKB: /usr/share/X11/locale/iso8859-15/Compose:48:29: too many errors
kwin_xkbcommon: XKB: /usr/share/X11/locale/iso8859-15/Compose:48:29: failed to parse file

I did not have these errors previously.

If I recompile libxkbcommon to set MAX_ERRORS to 1000, only 31 lines are not in error.
At that time I can enter circumflex and space and get circumflex but not
circumflex and a to get a circumflex.

I think the problem is in relation with kwin_xkbcommon but I don't know what to do.

I did a lot of searches, but i did not find an other user having the same problem.

Remark : I have no keyboard problem when I use xterm, thunderbird and firefox.

Thanks for any information