You are right, isn't a bug; thinking better I remember that at the end of installation, there was the folders in english and in italian in my home. Brobably confused and the first time with xfce, I deleted the wrong folders and/or renamed improperly. Deleting the command at login that I put some minutes ago the result is the same: thunar is and stay in italian.
Anyway, the output of commands that you suggest are:
$ cat /etc/sysconfig/i18n LANG="it_IT.UTF-8" SYSFONT="latarcyrheb-sun16"
Thunar --deamon is running at login and is running if thunar is closed.
Problem solved. Thanks again.