not local keyboard at login - cannot fix

at logging my keayboard is set to us when I'm using a french one and my prefs are (supposed to be?) set with this. Once in my session the keyboard setting is OK.

Only Apple technical note about this issue is referring to custom desktop pictures and I'm not using any.

I've tried logging in as root and alter root's prefs with no result.

Then I went the harsh way ( I've got another issue of Safari crashing at closure and other signs of corrupt system files, but re-installing OS X on the same drive didn't cure, obviously the faulty resources are retained in the re-install process).

I started up a new partition with fresh install and that was fine, it stopped being when I agreed on transferring system settings.

Which setting .plist .prefs file(s) should I delete then to get back to normal ?

Thanks